[Note that this file is a concatenation of more than one RFC.]
Internet Engineering Task Force (IETF) M. Cotton
Request for Comments: 6335 ICANN
BCP: 165 L. Eggert
Updates: 2780, 2782, 3828, 4340, 4960, 5595 Nokia
Category: Best Current Practice J. Touch
ISSN: 2070-1721 USC/ISI
M. Westerlund
Ericsson
S. Cheshire
Apple
August 2011
Internet Assigned Numbers Authority (IANA) Procedures for the Management
of the Service Name and Transport Protocol Port Number Registry
Abstract
This document defines the procedures that the Internet Assigned
Numbers Authority (IANA) uses when handling assignment and other
requests related to the Service Name and Transport Protocol Port
Number registry. It also discusses the rationale and principles
behind these procedures and how they facilitate the long-term
sustainability of the registry.
This document updates IANA's procedures by obsoleting the previous
UDP and TCP port assignment procedures defined in Sections 8 and 9.1
of the IANA Allocation Guidelines, and it updates the IANA service
name and port assignment procedures for UDP-Lite, the Datagram
Congestion Control Protocol (DCCP), and the Stream Control
Transmission Protocol (SCTP). It also updates the DNS SRV
specification to clarify what a service name is and how it is
registered.
Status of This Memo
This memo documents an Internet Best Current Practice.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6335.
Cotton, et al. Best Current Practice [Page 1]
RFC 6335 Service Name and Port Number Procedures August 2011
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
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RFC 6335 Service Name and Port Number Procedures August 2011
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Conventions Used in This Document . . . . . . . . . . . . . . 8
5. Service Names . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Service Name Syntax . . . . . . . . . . . . . . . . . . . 9
5.2. Service Name Usage in DNS SRV Records . . . . . . . . . . 10
6. Port Number Ranges . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Service Names and Port Numbers for Experimentation . . . . 12
7. Principles for Service Name and Transport Protocol Port
Number Registry Management . . . . . . . . . . . . . . . . . . 12
7.1. Past Principles . . . . . . . . . . . . . . . . . . . . . 13
7.2. Updated Principles . . . . . . . . . . . . . . . . . . . . 13
8. IANA Procedures for Managing the Service Name and
Transport Protocol Port Number Registry . . . . . . . . . . . 16
8.1. Service Name and Port Number Assignment . . . . . . . . . 16
8.2. Service Name and Port Number De-Assignment . . . . . . . . 21
8.3. Service Name and Port Number Reuse . . . . . . . . . . . . 21
8.4. Service Name and Port Number Revocation . . . . . . . . . 22
8.5. Service Name and Port Number Transfers . . . . . . . . . . 22
8.6. Maintenance Issues . . . . . . . . . . . . . . . . . . . . 23
8.7. Disagreements . . . . . . . . . . . . . . . . . . . . . . 23
9. Security Considerations . . . . . . . . . . . . . . . . . . . 23
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
10.1. Service Name Consistency . . . . . . . . . . . . . . . . . 24
10.2. Port Numbers for SCTP and DCCP Experimentation . . . . . . 26
10.3. Updates to DCCP Registries . . . . . . . . . . . . . . . . 27
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 28
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
13.1. Normative References . . . . . . . . . . . . . . . . . . . 29
13.2. Informative References . . . . . . . . . . . . . . . . . . 30
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RFC 6335 Service Name and Port Number Procedures August 2011
1. Introduction
For many years, the assignment of new service names and port number
values for use with the Transmission Control Protocol (TCP) [RFC0793]
and the User Datagram Protocol (UDP) [RFC0768] has had less than
clear guidelines. New transport protocols have been added -- the
Stream Control Transmission Protocol (SCTP) [RFC4960] and the
Datagram Congestion Control Protocol (DCCP) [RFC4342] -- and new
mechanisms like DNS SRV records [RFC2782] have been developed, each
with separate registries and separate guidelines. The community also
recognized the need for additional procedures beyond just assignment;
notably modification, revocation, and release.
A key element of the procedural streamlining specified in this
document is to establish identical assignment procedures for all IETF
transport protocols. This document brings the IANA procedures for
TCP and UDP in line with those for SCTP and DCCP, resulting in a
single process that requesters and IANA follow for all requests for
all transport protocols, including future protocols not yet defined.
In addition to detailing the IANA procedures for the initial
assignment of service names and port numbers, this document also
specifies post-assignment procedures that until now have been handled
in an ad hoc manner. These include procedures to de-assign a port
number that is no longer in use, to take a port number assigned for
one service that is no longer in use and reuse it for another
service, and the procedure by which IANA can unilaterally revoke a
prior port number assignment. Section 8 discusses the specifics of
these procedures and processes that requesters and IANA follow for
all requests for all current and future transport protocols.
IANA is the authority for assigning service names and port numbers.
The registries that are created to store these assignments are
maintained by IANA. For protocols developed by IETF working groups,
IANA now also offers a method for the "early assignment" [RFC4020] of
service names and port numbers, as described in Section 8.1.
This document updates IANA's procedures for UDP and TCP port numbers
by obsoleting Sections 8 and 9.1 of the IANA Allocation Guidelines
[RFC2780]. (Note that other sections of the IANA Allocation
Guidelines, relating to the protocol field values in IPv4 headers,
were also updated in February 2008 [RFC5237].) This document also
updates the IANA assignment procedures for DCCP [RFC4340] [RFC5595]
and SCTP [RFC4960].
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The Lightweight User Datagram Protocol (UDP-Lite) shares the port
space with UDP. The UDP-Lite specification [RFC3828] says: "UDP-Lite
uses the same set of port number values assigned by the IANA for use
by UDP". An update of the UDP procedures therefore also results in a
corresponding update of the UDP-Lite procedures.
This document also clarifies what a service name is and how it is
assigned. This will impact the DNS SRV specification [RFC2782],
because that specification merely makes a brief mention that the
symbolic names of services are defined in "Assigned Numbers"
[RFC1700], without stating to which section it refers within that
230-page document. The DNS SRV specification may have been referring
to the list of Port Assignments (known as /etc/services on Unix), or
to the "Protocol And Service Names" section, or to both, or to some
other section. Furthermore, "Assigned Numbers" [RFC1700] has been
obsoleted [RFC3232] and has been replaced by on-line registries
[PORTREG] [PROTSERVREG].
The development of new transport protocols is a major effort that the
IETF does not undertake very often. If a new transport protocol is
standardized in the future, it is expected to follow these guidelines
and practices around using service names and port numbers as much as
possible, for consistency.
At the time of writing of this document, the internal procedures of
"Expert Review" teams, including that of IANA's port review team, are
not documented in any RFC and this document doesn't change that.
2. Motivation
Information about the assignment procedures for the port registry has
existed in three locations: the forms for requesting port number
assignments on the IANA web site [SYSFORM] [USRFORM], an introductory
text section in the file listing the port number assignments
themselves (known as the port numbers registry) [PORTREG], and two
brief sections of the IANA Allocation Guidelines [RFC2780].
Similarly, the procedures surrounding service names have been
historically unclear. Service names were originally created as
mnemonic identifiers for port numbers without a well-defined syntax,
apart from the 14-character limit mentioned on the IANA website
[SYSFORM] [USRFORM]. Even that length limit has not been
consistently applied, and some assigned service names are 15
characters long. When service identification via DNS SRV Resource
Records (RRs) was introduced [RFC2782], it became useful to start
assigning service names alone, and because IANA had no procedure for
assigning a service name without an associated port number, this led
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RFC 6335 Service Name and Port Number Procedures August 2011
to the creation of an informal temporary service name registry
outside of the control of IANA, which now contains roughly 500
service names [SRVREG].
This document aggregates all this scattered information into a single
reference that aligns and clearly defines the management procedures
for both service names and port numbers. It gives more detailed
guidance to prospective requesters of service names and ports than
the existing documentation, and it streamlines the IANA procedures
for the management of the registry, so that requests can be completed
in a timely manner.
This document defines rules for assignment of service names without
associated port numbers, for such usages as DNS SRV records
[RFC2782], which was not possible under the previous IANA procedures.
The document also merges service name assignments from the non-IANA
ad hoc registry [SRVREG] and from the IANA Protocol and Service Names
registry [PROTSERVREG] into the IANA Service Name and Transport
Protocol Port Number registry [PORTREG], which from here on is the
single authoritative registry for service names and port numbers.
An additional purpose of this document is to describe the principles
that guide the IETF and IANA in their role as the long-term joint
stewards of the service name and port number registry. TCP and UDP
have had remarkable success over the last decades. Thousands of
applications and application-level protocols have service names and
port numbers assigned for their use, and there is every reason to
believe that this trend will continue into the future. It is hence
extremely important that management of the registry follow principles
that ensure its long-term usefulness as a shared resource. Section 7
discusses these principles in detail.
3. Background
The Transmission Control Protocol (TCP) [RFC0793] and the User
Datagram Protocol (UDP) [RFC0768] have enjoyed a remarkable success
over the decades as the two most widely used transport protocols on
the Internet. They have relied on the concept of "ports" as logical
entities for Internet communication. Ports serve two purposes:
first, they provide a demultiplexing identifier to differentiate
transport sessions between the same pair of endpoints, and second,
they may also identify the application protocol and associated
service to which processes connect. Newer transport protocols, such
as the Stream Control Transmission Protocol (SCTP) [RFC4960] and the
Datagram Congestion Control Protocol (DCCP) [RFC4342], have also
adopted the concept of ports for their communication sessions and use
16-bit port numbers in the same way as TCP and UDP (and UDP-Lite
[RFC3828], a variant of UDP).
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RFC 6335 Service Name and Port Number Procedures August 2011
Port numbers are the original and most widely used means for
application and service identification on the Internet. Ports are
16-bit numbers, and the combination of source and destination port
numbers together with the IP addresses of the communicating end
systems uniquely identifies a session of a given transport protocol.
Port numbers are also known by their associated service names such as
"telnet" for port number 23 and "http" (as well as "www" and
"www-http") for port number 80.
All involved parties -- hosts running services, hosts accessing
services on other hosts, and intermediate devices (such as firewalls
and NATs) that restrict services -- need to agree on which service
corresponds to a particular destination port. Although this is
ultimately a local decision with meaning only between the endpoints
of a connection, it is common for many services to have a default
port upon which those servers usually listen, when possible, and
these ports are recorded by the Internet Assigned Numbers Authority
(IANA) through the service name and port number registry [PORTREG].
Over time, the assumption that a particular port number necessarily
implies a particular service may become less true. For example,
multiple instances of the same service on the same host cannot
generally listen on the same port, and multiple hosts behind the same
NAT gateway cannot all have a mapping for the same port on the
external side of the NAT gateway, whether using static port mappings
configured by hand by the user, or dynamic port mappings configured
automatically using a port mapping protocol like the NAT Port Mapping
Protocol [NAT-PMP] or Internet Gateway Device [IGD].
Applications may use port numbers directly, look up port numbers
based on service names via system calls such as getservbyname() on
UNIX, look up port numbers by performing queries for DNS SRV records
[RFC2782] [DNS-SD], or determine port numbers in a variety of other
ways like the TCP Port Service Multiplexer (TCPMUX) [RFC1078].
Designers of applications and application-level protocols may apply
to IANA for an assigned service name and port number for a specific
application, and may -- after assignment -- assume that no other
application will use that service name or port number for its
communication sessions. Application designers also have the option
of requesting only an assigned service name without a corresponding
fixed port number if their application does not require one, such as
applications that use DNS SRV records to look up port numbers
dynamically at run-time. Because the port number space is finite
(and therefore conservation is an important goal), the alternative of
using service names instead of port numbers is RECOMMENDED whenever
possible.
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4. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
"Key words for use in RFCs to Indicate Requirement Levels" [RFC2119].
This document uses the term "assignment" to refer to the procedure by
which IANA provides service names and/or port numbers to requesting
parties; other RFCs refer to this as "allocation" or "registration".
This document assumes that all these terms have the same meaning, and
will use terms other than "assignment" only when quoting from or
referring to text in these other documents.
5. Service Names
Service names are the unique key in the Service Name and Transport
Protocol Port Number registry. This unique symbolic name for a
service may also be used for other purposes, such as in DNS SRV
records [RFC2782]. Within the registry, this unique key ensures that
different services can be unambiguously distinguished, thus
preventing name collisions and avoiding confusion about who is the
Assignee for a particular entry.
There may be more than one service name associated with a particular
transport protocol and port. There are three ways that such port
number overloading can occur:
o Overloading occurs when one service is an extension of another
service, and an in-band mechanism exists for determining if the
extension is present or not. One example is port 3478, which has
the service name aliases "stun" and "turn". Traversal Using
Relays around NAT (TURN) [RFC5766] is an extension to the Session
Traversal Utilities for NAT (STUN) [RFC5389] service. TURN-
enabled clients wishing to locate TURN servers could attempt to
discover "stun" services and then check in-band if the server also
supports TURN, but this would be inefficient. Enabling them to
directly query for "turn" servers by name is a better approach.
(Note that TURN servers in this case should also be locatable via
a "stun" discovery, because every TURN server is also a STUN
server.)
o By historical accident, the service name "http" has two synonyms
"www" and "www-http". When used in SRV records [RFC2782] and
similar service discovery mechanisms, only the service name "http"
should be used, not these additional names. If a server were to
advertise "www", it would not be discovered by clients browsing
for "http". Advertising or browsing for the aliases as well as
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the primary service name is inefficient, and achieves nothing that
is not already achieved by using the service name "http"
exclusively.
o As indicated in this document in Section 10.1, overloading has
been used to create replacement names that are consistent with the
syntax this document prescribes for legacy names that do not
conform to this syntax already. For such cases, only the new name
should be used in SRV records, to avoid the same issues as with
historical cases of multiple names, and also because the legacy
names are incompatible with SRV record use.
Assignment requests for new names for existing registered services
will be rejected, as a result. Implementers are requested to inform
IANA if they discover other cases where a single service has multiple
names, so that one name may be recorded as the primary name for
service discovery purposes.
Service names are assigned on a "first come, first served" basis, as
described in Section 8.1. Names should be brief and informative,
avoiding words or abbreviations that are redundant in the context of
the registry (e.g., "port", "service", "protocol", etc.) Names
referring to discovery services, e.g., using multicast or broadcast
to identify endpoints capable of a given service, SHOULD use an
easily identifiable suffix (e.g., "-disc").
5.1. Service Name Syntax
Valid service names are hereby normatively defined as follows:
o MUST be at least 1 character and no more than 15 characters long
o MUST contain only US-ASCII [ANSI.X3.4-1986] letters 'A' - 'Z' and
'a' - 'z', digits '0' - '9', and hyphens ('-', ASCII 0x2D or
decimal 45)
o MUST contain at least one letter ('A' - 'Z' or 'a' - 'z')
o MUST NOT begin or end with a hyphen
o hyphens MUST NOT be adjacent to other hyphens
The reason for requiring at least one letter is to avoid service
names like "23" (could be confused with a numeric port) or "6000-
6063" (could be confused with a numeric port range). Although
service names may contain both upper-case and lower-case letters,
case is ignored for comparison purposes, so both "http" and "HTTP"
denote the same service.
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Service names are purely opaque identifiers, and no semantics are
implied by any superficial structure that a given service name may
appear to have. For example, a company called "Example" may choose
to register service names "Example-Foo" and "Example-Bar" for its
"Foo" and "Bar" products, but the "Example" company cannot claim to
"own" all service names beginning with "Example-"; they cannot
prevent someone else from registering "Example-Baz" for a different
service, and they cannot prevent other developers from using the
"Example-Foo" and "Example-Bar" service types in order to
interoperate with the "Foo" and "Bar" products. Technically
speaking, in service discovery protocols, service names are merely a
series of byte values on the wire; for the mnemonic convenience of
human developers, it can be convenient to interpret those byte values
as human-readable ASCII characters, but software should treat them as
purely opaque identifiers and not attempt to parse them for any
additional embedded meaning.
As of August 5, 2009, approximately 98% of the so-called "Short
Names" [SYSFORM] [USRFORM] for existing port number assignments
[PORTREG] already met the rules for legal service names stated in
Section 8.1, and hence for these services their service name is
exactly the same as their historical "Short Name". In approximately
2% of cases, the new "service name" is derived based on the old
"Short Name" as described below in Section 10.1.
The rules for valid service names, excepting the limit of 15
characters maximum, are also expressed below (as a non-normative
convenience) using ABNF [RFC5234].
SRVNAME = *(1*DIGIT [HYPHEN]) ALPHA *([HYPHEN] ALNUM)
ALNUM = ALPHA / DIGIT ; A-Z, a-z, 0-9
HYPHEN = %x2D ; "-"
ALPHA = %x41-5A / %x61-7A ; A-Z / a-z [RFC5234]
DIGIT = %x30-39 ; 0-9 [RFC5234]
5.2. Service Name Usage in DNS SRV Records
The DNS SRV specification [RFC2782] states that the Service Label
part of the owner name of a DNS SRV record includes a "Service"
element, described as "the symbolic name of the desired service", but
as discussed above, it is not clear precisely what this means.
This document clarifies that the Service Label MUST be a service name
as defined herein with an underscore prepended. The service name
SHOULD be registered with IANA and recorded in the Service Name and
Transport Protocol Port Number registry [PORTREG].
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RFC 6335 Service Name and Port Number Procedures August 2011
The details of using Service Names in SRV Service Labels are
specified in the DNS SRV specification [RFC2782].
6. Port Number Ranges
TCP, UDP, UDP-Lite, SCTP, and DCCP use 16-bit namespaces for their
port number registries. The port registries for all of these
transport protocols are subdivided into three ranges of numbers
[RFC1340], and Section 8.1.2 describes the IANA procedures for each
range in detail:
o the System Ports, also known as the Well Known Ports, from 0-1023
(assigned by IANA)
o the User Ports, also known as the Registered Ports, from 1024-
49151 (assigned by IANA)
o the Dynamic Ports, also known as the Private or Ephemeral Ports,
from 49152-65535 (never assigned)
Of the assignable port ranges (System Ports and User Ports, i.e.,
port numbers 0-49151), individual port numbers are in one of three
states at any given time:
o Assigned: Assigned port numbers are currently assigned to the
service indicated in the registry.
o Unassigned: Unassigned port numbers are currently available for
assignment upon request, as per the procedures outlined in this
document.
o Reserved: Reserved port numbers are not available for regular
assignment; they are "assigned to IANA" for special purposes.
Reserved port numbers include values at the edges of each range,
e.g., 0, 1023, 1024, etc., which may be used to extend these
ranges or the overall port number space in the future.
In order to keep the size of the registry manageable, IANA typically
only records the Assigned and Reserved service names and port numbers
in the registry. Unassigned values are typically not explicitly
listed. (There are very many Unassigned service names and
enumerating them all would not be practical.)
As a data point, when this document was written, approximately 76% of
the TCP and UDP System Ports were assigned, and approximately 9% of
the User Ports were assigned. (As noted, Dynamic Ports are never
assigned.)
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6.1. Service Names and Port Numbers for Experimentation
Of the System Ports, two TCP and UDP port numbers (1021 and 1022),
together with their respective service names ("exp1" and "exp2"),
have been assigned for experimentation with new applications and
application-layer protocols that require a port number in the
assigned ports range [RFC4727].
Please refer to Sections 1 and 1.1 of "Assigning Experimental and
Testing Numbers Considered Useful" [RFC3692] for how these
experimental port numbers are to be used.
This document assigns the same two service names and port numbers for
experimentation with new application-layer protocols over SCTP and
DCCP in Section 10.2.
Unfortunately, it can be difficult to limit access to these ports.
Users SHOULD take measures to ensure that experimental ports are
connecting to the intended process. For example, users of these
experimental ports might include a 64-bit nonce, once on each segment
of a message-oriented channel (e.g., UDP), or once at the beginning
of a byte-stream (e.g., TCP), which is used to confirm that the port
is being used as intended. Such confirmation of intended use is
especially important when these ports are associated with privileged
(e.g., system or administrator) processes.
7. Principles for Service Name and Transport Protocol Port Number
Registry Management
Management procedures for the Service Name and Transport Protocol
Port Number registry include assignment of service names and port
numbers upon request, as well as management of information about
existing assignments. The latter includes maintaining contact and
description information about assignments, revoking abandoned
assignments, and redefining assignments when needed. Of these
procedures, careful port number assignment is most critical, in order
to continue to conserve the remaining port numbers.
As noted earlier, only about 9% of the User Port space is currently
assigned. The current rate of assignment is approximately 400 ports
per year, and has remained steady for the past 8 years. At that
rate, if similar conservation continues, this resource will sustain
another 85 years of assignment - without the need to resort to
reassignment of released values or revocation. The namespace
available for service names is much larger, which allows for simpler
management procedures.
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7.1. Past Principles
The principles for service name and port number management are based
on the recommendations of the IANA "Expert Review" team. Until
recently, that team followed a set of informal guidelines developed
based on the review experience from previous assignment requests.
These original guidelines, although informal, had never been publicly
documented. They are recorded here for historical purposes only; the
current guidelines are described in Section 7.2. These guidelines
previously were:
o TCP and UDP ports were simultaneously assigned when either was
requested
o Port numbers were the primary assignment; service names were
informative only, and did not have a well-defined syntax
o Port numbers were conserved informally, and sometimes
inconsistently (e.g., some services were assigned ranges of many
port numbers even where not strictly necessary)
o SCTP and DCCP service name and port number registries were managed
separately from the TCP/UDP registries
o Service names could not be assigned in the old ports registry
without assigning an associated port number at the same time
7.2. Updated Principles
This section summarizes the current principles by which IANA both
handles the Service Name and Transport Protocol Port Number registry
and attempts to conserve the port number space. This description is
intended to inform applicants requesting service names and port
numbers. IANA has flexibility beyond these principles when handling
assignment requests; other factors may come into play, and exceptions
may be made to best serve the needs of the Internet. Applicants
should be aware that IANA decisions are not required to be bound to
these principles. These principles and general advice to users on
port use are expected to change over time.
IANA strives to assign service names that do not request an
associated port number assignment under a simple "First Come First
Served" policy [RFC5226]. IANA MAY, at its discretion, refer service
name requests to "Expert Review" in cases of mass assignment requests
or other situations where IANA believes "Expert Review" is advisable
[RFC5226]; use of the "Expert Review" helps advise IANA informally in
cases where "IETF Review" or "IESG Approval" is used, as with most
IETF protocols.
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RFC 6335 Service Name and Port Number Procedures August 2011
The basic principle of service name and port number registry
management is to conserve use of the port space where possible.
Extensions to support larger port number spaces would require
changing many core protocols of the current Internet in a way that
would not be backward compatible and interfere with both current and
legacy applications.
Conservation of the port number space is required because this space
is a limited resource, so applications are expected to participate in
the traffic demultiplexing process where feasible. The port numbers
are expected to encode as little information as possible that will
still enable an application to perform further demultiplexing by
itself. In particular, the principles form a goal that IANA strives
to achieve for new applications (with exceptions as deemed
appropriate, especially as for extensions to legacy services) as
follows:
o IANA strives to assign only one assigned port number per service
or application.
Note: At the time of writing of this document, there is no IETF
consensus on when it is appropriate to use a second port for an
insecure version of a protocol.
o IANA strives to assign only one assigned port number for all
variants of a service (e.g., for updated versions of a service).
o IANA strives to encourage the deployment of secure protocols.
o IANA strives to assign only one assigned port number for all
different types of devices using or participating in the same
service.
o IANA strives to assign port numbers only for the transport
protocol(s) explicitly named in an assignment request.
o IANA may recover unused port numbers, via the new procedures of
de-assignment, revocation, and transfer.
Where possible, a given service is expected to demultiplex messages
if necessary. For example, applications and protocols are expected
to include in-band version information, so that future versions of
the application or protocol can share the same assigned port.
Applications and protocols are also expected to be able to
efficiently use a single assigned port for multiple sessions, either
by demultiplexing multiple streams within one port or by using the
assigned port to coordinate using dynamic ports for subsequent
exchanges (e.g., in the spirit of FTP [RFC0959]).
Cotton, et al. Best Current Practice [Page 14]
RFC 6335 Service Name and Port Number Procedures August 2011
Ports are used in various ways, notably:
o as endpoint process identifiers
o as application protocol identifiers
o for firewall-filtering purposes
Both the process-identifier and the protocol-identifier uses suggest
that anything a single process can demultiplex, or that can be
encoded into a single protocol, should be. The firewall-filtering
use suggests that some uses that could be multiplexed or encoded
could instead be separated to allow for easier firewall management.
Note that this latter use is much less sound, because port numbers
have meaning only for the two endpoints involved in a connection, and
drawing conclusions about the service that generated a given flow
based on observed port numbers is not always reliable.
Effective with the publication of this document, IANA will begin
assigning port numbers for only those transport protocols explicitly
included in an assignment request. This ends the long-standing
practice of automatically assigning a port number to an application
for both TCP and UDP, even if the request is for only one of these
transport protocols. The new assignment procedure conserves
resources by assigning a port number to an application for only those
transport protocols (TCP, UDP, SCTP, and/or DCCP) it actually uses.
The port number will be marked as Reserved -- instead of Assigned --
in the port number registries of the other transport protocols. When
applications start supporting the use of some of those additional
transport protocols, the Assignee for the assignment MUST request
that IANA convert these reserved ports into assignments. An
application MUST NOT assume that it can use a port number assigned to
it for use with one transport protocol with another transport
protocol without IANA converting the reservation into an assignment.
When the available pool of unassigned numbers has run out in a port
range, it will be necessary for IANA to consider the Reserved ports
for assignment. This is part of the motivation for not automatically
assigning ports for transport protocols other than the requested
one(s). This will allow more ports to be available for assignment at
that point. To help conserve ports, application developers SHOULD
request assignment of only those transport protocols that their
application currently uses.
Conservation of port numbers is improved by procedures that allow
previously assigned port numbers to become Unassigned, either through
de-assignment or through revocation, and by a procedure that lets
application designers transfer an assigned but unused port number to
Cotton, et al. Best Current Practice [Page 15]
RFC 6335 Service Name and Port Number Procedures August 2011
a new application. Section 8 describes these procedures, which until
now were undocumented. Port number conservation is also improved by
recommending that applications that do not require an assigned port
should register only a service name without an associated port
number.
8. IANA Procedures for Managing the Service Name and Transport Protocol
Port Number Registry
This section describes the process for handling requests associated
with IANA's management of the Service Name and Transport Protocol
Port Number registry. Such requests include initial assignment, de-
assignment, reuse, and updates to the contact information or
description associated with an assignment. Revocation is an
additional process, initiated by IANA.
8.1. Service Name and Port Number Assignment
Assignment refers to the process of providing service names or port
numbers to applicants. All such assignments are made from service
names or port numbers that are Unassigned or Reserved at the time of
the assignment.
o Unassigned names and numbers are assigned according to the rules
described in Section 8.1.2 below.
o Reserved numbers and names are generally only assigned by a
"Standards Action" or "IESG Approval", and MUST be accompanied by
a statement explaining the reason a Reserved number or name is
appropriate for this action. The only exception to this rule is
that the current Assignee of a port number MAY request the
assignment of the corresponding Reserved port number for other
transport protocols when needed. IANA will initiate an "Expert
Review" [RFC5226] for such requests.
When an assignment for one or more transport protocols is approved,
the port number for any non-requested transport protocol(s) will be
marked as Reserved. IANA SHOULD NOT assign that port number to any
other application or service until no other port numbers remain
Unassigned in the requested range. It is anticipated that at such
time a new document will be published specifying IANA procedures for
assignment of such ports.
Cotton, et al. Best Current Practice [Page 16]
RFC 6335 Service Name and Port Number Procedures August 2011
8.1.1. General Assignment Procedure
A service name or port number assignment request contains the
following information. The service name is the unique identifier of
a given service:
Service Name (REQUIRED)
Transport Protocol(s) (REQUIRED)
Assignee (REQUIRED)
Contact (REQUIRED)
Description (REQUIRED)
Reference (REQUIRED)
Port Number (OPTIONAL)
Service Code (REQUIRED for DCCP only)
Known Unauthorized Uses (OPTIONAL)
Assignment Notes (OPTIONAL)
o Service Name: A desired unique service name for the service
associated with the assignment request MUST be provided. This
name may be used with various service selection and discovery
mechanisms (including, but not limited to, DNS SRV records
[RFC2782]). The name MUST be compliant with the syntax defined in
Section 5.1. In order to be unique, they MUST NOT be identical to
any currently assigned service name in the IANA registry
[PORTREG]. Service names are case-insensitive; they may be
provided and entered into the registry with mixed case for
clarity, but case is ignored otherwise.
o Transport Protocol(s): The transport protocol(s) for which an
assignment is requested MUST be provided. This field is currently
limited to one or more of TCP, UDP, SCTP, and DCCP. Requests
without any port assignment and only a service name are still
required to indicate which protocol the service uses.
o Assignee: Name and email address of the party to whom the
assignment is made. This is REQUIRED. The Assignee is the
organization, company or individual person responsible for the
initial assignment. For assignments done through RFCs published
via the "IETF Document Stream" [RFC4844], the Assignee will be the
IESG <iesg@ietf.org>.
o Contact: Name and email address of the Contact person for the
assignment. This is REQUIRED. The Contact person is the
responsible person for the Internet community to send questions
to. This person is also authorized to submit changes on behalf of
the Assignee; in cases of conflict between the Assignee and the
Contact, the Assignee decisions take precedence. Additional
Cotton, et al. Best Current Practice [Page 17]
RFC 6335 Service Name and Port Number Procedures August 2011
address information MAY be provided. For assignments done through
RFCs published via the "IETF Document Stream" [RFC4844], the
Contact will be the IETF Chair <chair@ietf.org>.
o Description: A short description of the service associated with
the assignment request is REQUIRED. It should avoid all but the
most well-known acronyms.
o Reference: A description of (or a reference to a document
describing) the protocol or application using this port. This is
REQUIRED. The description must state whether the protocol uses
IP-layer broadcast, multicast, or anycast communication.
For assignments requesting only a Service Name, or a Service Name
and User Port, a statement that the protocol is proprietary and
not publicly documented is also acceptable, provided that the
required information regarding the use of IP broadcast, multicast,
or anycast is given.
For any assignment request that includes a User Port, the
assignment request MUST explain why a port number in the Dynamic
Ports range (discovered by clients dynamically at run-time) is
unsuitable for the given application.
For any assignment request that includes a System Port, the
assignment request MUST explain why a port number in the User
Ports or Dynamic Ports ranges is unsuitable, and a reference to a
stable protocol specification document MUST be provided.
IANA MAY accept early assignment [RFC4020] requests (known as
"early allocation" therein) from IETF working groups that
reference a sufficiently stable Internet-Draft instead of a
published Standards-Track RFC.
o Port Number: If assignment of a port number is desired, either the
port number the requester suggests for assignment or indication of
port range (user or system) MUST be provided. If only a service
name is to be assigned, this field is left empty. If a specific
port number is requested, IANA is encouraged to assign the
requested number. If a range is specified, IANA will choose a
suitable number from the User or System Ports ranges. Note that
the applicant MUST NOT use the requested port in implementations
deployed for use on the public Internet prior to the completion of
the assignment, because there is no guarantee that IANA will
assign the requested port.
Cotton, et al. Best Current Practice [Page 18]
RFC 6335 Service Name and Port Number Procedures August 2011
o Service Code: If the assignment request includes DCCP as a
transport protocol, then the request MUST include a desired unique
DCCP service code [RFC5595], and MUST NOT include a requested DCCP
service code otherwise. Section 19.8 of the DCCP specification
[RFC4340] defines requirements and rules for assignment, updated
by this document. Note that, as per the DCCP Service Codes
document [RFC5595], some service codes are not assigned; zero
(absence of a meaningful service code) and 4294967295 (0xFFFFFFFF;
invalid service code) are permanently reserved, and the Private
service codes 1056964608-1073741823 (0x3F000000-0x3FFFFFFF; i.e.,
32-bit values with the high-order byte equal to a value of 63
(0x3F), corresponding to the ASCII character '?') are not
centrally assigned.
o Known Unauthorized Uses: A list of uses by applications or
organizations who are not the Assignee. This is OPTIONAL. This
list may be augmented by IANA after assignment when unauthorized
uses are reported.
o Assignment Notes: Indications of owner/name change, or any other
assignment process issue. This is OPTIONAL. This list may be
updated by IANA after assignment to help track changes to an
assignment, e.g., de-assignment, owner/name changes, etc.
If the assignment request is for the addition of a new transport
protocol to a previously assigned service name and the requester is
not the Assignee or Contact for the previously assigned service name,
IANA needs to confirm with the Assignee for the existing assignment
whether this addition is appropriate.
If the assignment request is for a new service name sharing the same
port as a previously assigned service name (see port number
overloading in Section 5), IANA needs to confirm with the Assignee
for the existing service name and other appropriate experts whether
the overloading is appropriate.
When IANA receives an assignment request -- containing the above
information -- that is requesting a port number, IANA SHALL initiate
an "Expert Review" [RFC5226] in order to determine whether an
assignment should be made. For requests that are not seeking a port
number, IANA SHOULD assign the service name under a simple "First
Come First Served" policy [RFC5226].
Cotton, et al. Best Current Practice [Page 19]
RFC 6335 Service Name and Port Number Procedures August 2011
8.1.2. Variances for Specific Port Number Ranges
Section 6 describes the different port number ranges. It is
important to note that IANA applies slightly different procedures
when managing the different port ranges of the service name and port
number registry:
o Ports in the Dynamic Ports range (49152-65535) have been
specifically set aside for local and dynamic use and cannot be
assigned through IANA. Application software may simply use any
dynamic port that is available on the local host, without any sort
of assignment. On the other hand, application software MUST NOT
assume that a specific port number in the Dynamic Ports range will
always be available for communication at all times, and a port
number in that range hence MUST NOT be used as a service
identifier.
o Ports in the User Ports range (1024-49151) are available for
assignment through IANA, and MAY be used as service identifiers
upon successful assignment. Because assigning a port number for a
specific application consumes a fraction of the shared resource
that is the port number registry, IANA will require the requester
to document the intended use of the port number. For most IETF
protocols, ports in the User Ports range will be assigned under
the "IETF Review" or "IESG Approval" procedures [RFC5226] and no
further documentation is required. Where these procedures do not
apply, then the requester must input the documentation to the
"Expert Review" procedure [RFC5226], by which IANA will have a
technical expert review the request to determine whether to grant
the assignment. Regardless of the path ("IETF Review", "IESG
Approval", or "Expert Review"), the submitted documentation is
expected to be the same, as described in this section, and MUST
explain why using a port number in the Dynamic Ports range is
unsuitable for the given application. Further, IANA MAY utilize
the "Expert Review" process informally to inform their position in
participating in "IETF Review" and "IESG Approval".
o Ports in the System Ports range (0-1023) are also available for
assignment through IANA. Because the System Ports range is both
the smallest and the most densely assigned, the requirements for
new assignments are more strict than those for the User Ports
range, and will only be granted under the "IETF Review" or "IESG
Approval" procedures [RFC5226]. A request for a System Port
number MUST document *both* why using a port number from the
Dynamic Ports range is unsuitable *and* why using a port number
from the User Ports range is unsuitable for that application.
Cotton, et al. Best Current Practice [Page 20]
RFC 6335 Service Name and Port Number Procedures August 2011
8.2. Service Name and Port Number De-Assignment
The Assignee of a granted port number assignment can return the port
number to IANA at any time if they no longer have a need for it. The
port number will be de-assigned and will be marked as Reserved. IANA
should not reassign port numbers that have been de-assigned until all
unassigned port numbers in the specific range have been assigned.
Before proceeding with a port number de-assignment, IANA needs to
reasonably establish that the value is actually no longer in use.
Because there is much less danger of exhausting the service name
space compared to the port number space, it is RECOMMENDED that a
given service name remain assigned even after all associated port
number assignments have become de-assigned. Under this policy, it
will appear in the registry as if it had been created through a
service name assignment request that did not include any port
numbers.
On rare occasions, it may still be useful to de-assign a service
name. In such cases, IANA will mark the service name as Reserved.
IANA will involve their IESG-appointed expert in such cases.
IANA will include a comment in the registry when de-assignment
happens to indicate its historic usage.
8.3. Service Name and Port Number Reuse
If the Assignee of a granted port number assignment no longer has a
need for the assigned number, but would like to reuse it for a
different application, they can submit a request to IANA to do so.
Logically, port number reuse is to be thought of as a de-assignment
(Section 8.2) followed by an immediate (re-)assignment (Section 8.1)
of the same port number for a new application. Consequently, the
information that needs to be provided about the proposed new use of
the port number is identical to what would need to be provided for a
new port number assignment for the specific ports range.
Because there is much less danger of exhausting the service name
space compared to the port number space, it is RECOMMENDED that the
original service name associated with the prior use of the port
number remains assigned, and a new service name be created and
associated with the port number. This is again consistent with
viewing a reuse request as a de-assignment followed by an immediate
(re-)assignment. Reusing an assigned service name for a different
application is NOT RECOMMENDED.
Cotton, et al. Best Current Practice [Page 21]
RFC 6335 Service Name and Port Number Procedures August 2011
IANA needs to carefully review such requests before approving them.
In some instances, the Expert Reviewer will determine that the
application the port number was assigned to has found usage beyond
the original Assignee, or that there is a concern that it may have
such users. This determination MUST be made quickly. A community
call concerning revocation of a port number (see below) MAY be
considered, if a broader use of the port number is suspected.
8.4. Service Name and Port Number Revocation
A port number revocation can be thought of as an IANA-initiated de-
assignment (Section 8.2), and has exactly the same effect on the
registry.
Sometimes, it will be clear that a specific port number is no longer
in use and that IANA can revoke it and mark it as Reserved. At other
times, it may be unclear whether a given assigned port number is
still in use somewhere in the Internet. In those cases, IANA must
carefully consider the consequences of revoking the port number, and
SHOULD only do so if there is an overwhelming need.
With the help of their IESG-appointed Expert Reviewer, IANA SHALL
formulate a request to the IESG to issue a four-week community call
concerning the pending port number revocation. The IESG and IANA,
with the Expert Reviewer's support, SHALL determine promptly after
the end of the community call whether revocation should proceed, and
then communicate their decision to the community. This procedure
typically involves similar steps to de-assignment except that it is
initiated by IANA.
Because there is much less danger of exhausting the service name
space compared to the port number space, revoking service names is
NOT RECOMMENDED.
8.5. Service Name and Port Number Transfers
The value of service names and port numbers is defined by their
careful management as a shared Internet resource, whereas enabling
transfer allows the potential for associated monetary exchanges. As
a result, the IETF does not permit service name or port number
assignments to be transferred between parties, even when they are
mutually consenting.
The appropriate alternate procedure is a coordinated de-assignment
and assignment: The new party requests the service name or port
number via an assignment and the previous party releases its
assignment via the de-assignment procedure outlined above.
Cotton, et al. Best Current Practice [Page 22]
RFC 6335 Service Name and Port Number Procedures August 2011
With the help of their IESG-appointed Expert Reviewer, IANA SHALL
carefully determine if there is a valid technical, operational, or
managerial reason to grant the requested new assignment.
8.6. Maintenance Issues
In addition to the formal procedures described above, updates to the
Description and Contact information are coordinated by IANA in an
informal manner, and may be initiated by either the Assignee or by
IANA, e.g., by the latter requesting an update to current Contact
information. (Note that the Assignee cannot be changed as a separate
procedure; see instead Section 8.5 above.)
8.7. Disagreements
In the case of disagreements around any request, there is the
possibility of appeal following the normal appeals process for IANA
assignments as defined by Section 7 of "Guidelines for Writing an
IANA Considerations Section in RFCs" [RFC5226].
9. Security Considerations
The IANA guidelines described in this document do not change the
security properties of UDP, TCP, SCTP, or DCCP.
Assignment of a service name or port number does not in any way imply
an endorsement of an application or product, and the fact that
network traffic is flowing to or from an assigned port number does
not mean that it is "good" traffic, or even that it is used by the
assigned service. Firewall and system administrators should choose
how to configure their systems based on their knowledge of the
traffic in question, not based on whether or not there is an assigned
service name or port number.
Services are expected to include support for security, either as
default or dynamically negotiated in-band. The use of separate
service name or port number assignments for secure and insecure
variants of the same service is to be avoided in order to discourage
the deployment of insecure services.
Cotton, et al. Best Current Practice [Page 23]
RFC 6335 Service Name and Port Number Procedures August 2011
10. IANA Considerations
This document obsoletes Sections 8 and 9.1 of the March 2000 IANA
Allocation Guidelines [RFC2780].
Upon approval of this document for publication as an RFC, IANA worked
with Stuart Cheshire, maintainer of the independent service name
registry [SRVREG], to merge the contents of that private registry
into the official IANA registry. The independent registry web page
has been updated with pointers to the IANA registry and to this RFC.
IANA created a new service name entry in the service name and port
number registry [PORTREG] for all entries in the Protocol and Service
Names registry [PROTSERVREG] that did not already have one assigned.
IANA also indicates in the Assignment Notes for "www" and "www-http"
that they are duplicate terms that refer to the "http" service, and
should not be used for discovery purposes. For this conceptual
service (human-readable web pages served over HTTP), the correct
service name to use for service discovery purposes is "http" (see
Section 5).
10.1. Service Name Consistency
Section 8.1 defines which character strings are well-formed service
names, which until now had not been clearly defined. The definition
in Section 8.1 was chosen to allow maximum compatibility of service
names with current and future service discovery mechanisms.
As of August 5, 2009, approximately 98% of the so-called "Short
Names" from existing port number assignments [PORTREG] met the rules
for legal service names stated in Section 8.1, and hence for these
services their service name is exactly the same as their "Short
Name".
The remaining approximately 2% of the existing "Short Names" are not
suitable to be used directly as well-formed service names because
they contain illegal characters such as asterisks, dots, pluses,
slashes, or underscores. All existing "Short Names" conform to the
length requirement of 15 characters or fewer. For these 96
unsuitable "Short Names", listed in the table below, the service name
is the Short Name with any illegal characters replaced by hyphens.
IANA added an entry to the registry that uses the new well-formed
primary service name for the existing service and that otherwise
duplicates the original assignment information. In the description
field of this new entry giving the primary service name, IANA
recorded that it has assigned a well-formed service name for the
previous service and references the original assignment. In the
Cotton, et al. Best Current Practice [Page 24]
RFC 6335 Service Name and Port Number Procedures August 2011
Assignment Notes field of the original assignment, IANA added a note
that this entry is an alias to the new well-formed service name, and
that the old service name is historic, not usable for use with many
common service discovery mechanisms.
96 names containing illegal characters to be replaced by hyphens:
+----------------+-----------------+-----------------+
| 914c/g | acmaint_dbd | acmaint_transd |
| atex_elmd | avanti_cdp | badm_priv |
| badm_pub | bdir_priv | bdir_pub |
| bmc_ctd_ldap | bmc_patroldb | boks_clntd |
| boks_servc | boks_servm | broker_service |
| bues_service | canit_store | cedros_fds |
| cl/1 | contamac_icm | corel_vncadmin |
| csc_proxy | cvc_hostd | dbcontrol_agent |
| dec_dlm | dl_agent | documentum_s |
| dsmeter_iatc | dsx_monitor | elpro_tunnel |
| elvin_client | elvin_server | encrypted_admin |
| erunbook_agent | erunbook_server | esri_sde |
| EtherNet/IP-1 | EtherNet/IP-2 | event_listener |
| flr_agent | gds_db | ibm_wrless_lan |
| iceedcp_rx | iceedcp_tx | iclcnet_svinfo |
| idig_mux | ife_icorp | instl_bootc |
| instl_boots | intel_rci | interhdl_elmd |
| lan900_remote | LiebDevMgmt_A | LiebDevMgmt_C |
| LiebDevMgmt_DM | mapper-ws_ethd | matrix_vnet |
| mdbs_daemon | menandmice_noh | msl_lmd |
| nburn_id | ncr_ccl | nds_sso |
| netmap_lm | nms_topo_serv | notify_srvr |
| novell-lu6.2 | nuts_bootp | nuts_dem |
| ocs_amu | ocs_cmu | pipe_server |
| pra_elmd | printer_agent | redstorm_diag |
| redstorm_find | redstorm_info | redstorm_join |
| resource_mgr | rmonitor_secure | rsvp_tunnel |
| sai_sentlm | sge_execd | sge_qmaster |
| shiva_confsrvr | sql*net | srvc_registry |
| stm_pproc | subntbcst_tftp | udt_os |
| universe_suite | veritas_pbx | vision_elmd |
| vision_server | wrs_registry | z39.50 |
+----------------+-----------------+-----------------+
In addition to the 96 names listed above, the service name for
"whois++" is "whoispp", following the example set by the
"application/whoispp-query" MIME Content-Type [RFC2957].
Cotton, et al. Best Current Practice [Page 25]
RFC 6335 Service Name and Port Number Procedures August 2011
There were four names recorded in IANA's Port Number Registry
[PORTREG] that conflicted with names previously recorded in the ad
hoc SRV name registry [SRVREG]: esp, hydra, recipe, and xmp.
The name conflicts were resolved amicably:
The IANA Port Number Registry Short Name "esp" had been registered by
Andrew Chernow, and he informed the authors that the port was no
longer in use and the registration was no longer required. The SRV
registry entry for "esp" remains in effect.
The SRV name "hydra" for SubEthaEdit had already been retired in
favor of the new SRV name "see". The IANA Port Number Registry entry
for "hydra" remains in effect.
The SRV name "recipe" was in use in an open source project that had
not yet been packaged for distribution, and the registrant Daniel
Taylor was willing to change to a different service name. Thanks to
Daniel Taylor for accommodating this change. The IANA Port Number
Registry entry for "recipe" remains in effect.
The IANA Port Number Registry Short Name "xmp" had been registered by
Bobby Krupczak, but since his registration included an assigned port
number (which is still in use and remains unaffected by this change),
he was willing to switch to a different service name. Thanks to
Bobby Krupczak for accommodating this change. The SRV registry entry
for "xmp" remains in effect.
10.2. Port Numbers for SCTP and DCCP Experimentation
Two System UDP and TCP ports, 1021 and 1022, have been reserved for
experimental use [RFC4727]. This document assigns the same port
numbers for SCTP and DCCP, updates the TCP and UDP assignments, and
also instructs IANA to automatically assign these two port numbers
for any future transport protocol with a similar 16-bit port number
namespace.
Note that these port numbers are meant for temporary experimentation
and development in controlled environments. Before using these port
numbers, carefully consider the advice in Section 6.1 in this
document, as well as in Sections 1 and 1.1 of "Assigning Experimental
and Testing Numbers Considered Useful" [RFC3692]. Most importantly,
application developers must request a permanent port number
assignment from IANA as described in Section 8.1 before any kind of
non-experimental deployment.
Cotton, et al. Best Current Practice [Page 26]
RFC 6335 Service Name and Port Number Procedures August 2011
+--------------------+-----------------------------+
| Service Name | exp1 |
| Transport Protocol | DCCP, SCTP, TCP, UDP |
| Assignee | IESG <iesg@ietf.org> |
| Contact | IETF Chair <chair@ietf.org> |
| Description | RFC3692-style Experiment 1 |
| Reference | [RFC4727] [RFC6335] |
| Port Number | 1021 |
+--------------------+-----------------------------+
+--------------------+-----------------------------+
| Service Name | exp2 |
| Transport Protocol | DCCP, SCTP, TCP, UDP |
| Assignee | IESG <iesg@ietf.org> |
| Contact | IETF Chair <chair@ietf.org> |
| Description | RFC3692-style Experiment 2 |
| Reference | [RFC4727] [RFC6335] |
| Port Number | 1022 |
+--------------------+-----------------------------+
10.3. Updates to DCCP Registries
This document updates the IANA assignment procedures for the DCCP
Port Number and DCCP Service Codes Registries [RFC4340].
10.3.1. DCCP Service Code Registry
Service codes are assigned on a "first come, first served" basis
according to Section 19.8 of the DCCP specification [RFC4340]. This
document updates that section by extending the guidelines given there
in the following ways:
o IANA MAY assign new service codes without seeking "Expert Review"
using their discretion, but SHOULD seek "Expert Review" if a
request asks for more than five service codes.
o IANA should feel free to contact the DCCP Expert Reviewer with any
questions related to requests for DCCP-related codepoints.
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RFC 6335 Service Name and Port Number Procedures August 2011
10.3.2. DCCP Port Numbers Registry
The DCCP ports registry is defined by Section 19.9 of the DCCP
specification [RFC4340]. Assignments in this registry require prior
assignment of a service code. Not all service codes require IANA-
assigned ports. This document updates that section by extending the
guidelines given there in the following way:
o IANA should normally assign a value in the range 1024-49151 to a
DCCP server port. IANA requests to assign port numbers in the
System Ports range (0 through 1023) require an "IETF Review"
[RFC5226] prior to assignment by IANA [RFC4340].
o IANA MUST NOT assign more than one DCCP server port to a single
service code value.
o The assignment of multiple service codes to the same DCCP port is
allowed, but subject to "Expert Review".
o The set of service code values associated with a DCCP server port
should be recorded in the service name and port number registry.
o A request for additional service codes to be associated with an
already assigned port number requires "Expert Review". These
requests will normally be accepted when they originate from the
contact associated with the port assignment. In other cases,
these applications will be expected to use an unassigned port,
when this is available.
The DCCP specification [RFC4340] notes that a short port name MUST be
associated with each DCCP server port that has been assigned. This
document clarifies that this short port name is the service name as
defined here, and this name MUST be unique.
11. Contributors
Alfred Hoenes (ah@tr-sys.de) and Allison Mankin (mankin@psg.com) have
contributed text and ideas to this document.
12. Acknowledgments
The text in Section 10.3 is based on a suggestion originally proposed
as a part of the DCCP Service Codes document [RFC5595] by Gorry
Fairhurst.
Lars Eggert is partly funded by the Trilogy Project [TRILOGY], a
research project supported by the European Commission under its
Seventh Framework Program.
Cotton, et al. Best Current Practice [Page 28]
RFC 6335 Service Name and Port Number Procedures August 2011
13. References
13.1. Normative References
[ANSI.X3.4-1986] American National Standards Institute, "Coded
Character Set - 7-bit American Standard Code for
Information Interchange", ANSI X3.4, 1986.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6,
RFC 768, August 1980.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2780] Bradner, S. and V. Paxson, "IANA Allocation
Guidelines For Values In the Internet Protocol and
Related Headers", BCP 37, RFC 2780, March 2000.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS
RR for specifying the location of services (DNS
SRV)", RFC 2782, February 2000.
[RFC3828] Larzon, L-A., Degermark, M., Pink, S., Jonsson,
L-E., and G. Fairhurst, "The Lightweight User
Datagram Protocol (UDP-Lite)", RFC 3828, July 2004.
[RFC4020] Kompella, K. and A. Zinin, "Early IANA Allocation
of Standards Track Code Points", BCP 100, RFC 4020,
February 2005.
[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", RFC 4340,
March 2006.
[RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6,
ICMPv4, ICMPv6, UDP, and TCP Headers", RFC 4727,
November 2006.
[RFC4960] Stewart, R., "Stream Control Transmission
Protocol", RFC 4960, September 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for
Writing an IANA Considerations Section in RFCs",
BCP 26, RFC 5226, May 2008.
Cotton, et al. Best Current Practice [Page 29]
RFC 6335 Service Name and Port Number Procedures August 2011
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234,
January 2008.
[RFC5595] Fairhurst, G., "The Datagram Congestion Control
Protocol (DCCP) Service Codes", RFC 5595,
September 2009.
13.2. Informative References
[DNS-SD] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", Work in Progress, February 2011.
[IGD] UPnP Forum, "Internet Gateway Device (IGD) V 1.0",
November 2001.
[NAT-PMP] Cheshire, S., "NAT Port Mapping Protocol (NAT-
PMP)", Work in Progress, April 2008.
[PORTREG] Internet Assigned Numbers Authority (IANA),
"Service Name and Transport Protocol Port Number
Registry",
<http://www.iana.org/assignments/port-numbers>.
[PROTSERVREG] Internet Assigned Numbers Authority (IANA),
"Protocol and Service Names Registry",
<http://www.iana.org/assignments/service-names>.
[RFC0959] Postel, J. and J. Reynolds, "File Transfer
Protocol", STD 9, RFC 959, October 1985.
[RFC1078] Lottor, M., "TCP port service Multiplexer
(TCPMUX)", RFC 1078, November 1988.
[RFC1340] Reynolds, J. and J. Postel, "Assigned Numbers",
RFC 1340, July 1992.
[RFC1700] Reynolds, J. and J. Postel, "Assigned Numbers",
RFC 1700, October 1994.
[RFC2957] Daigle, L. and P. Faltstrom, "The application/
whoispp-query Content-Type", RFC 2957,
October 2000.
[RFC3232] Reynolds, J., "Assigned Numbers: RFC 1700 is
Replaced by an On-line Database", RFC 3232,
January 2002.
Cotton, et al. Best Current Practice [Page 30]
RFC 6335 Service Name and Port Number Procedures August 2011
[RFC3692] Narten, T., "Assigning Experimental and Testing
Numbers Considered Useful", BCP 82, RFC 3692,
January 2004.
[RFC4342] Floyd, S., Kohler, E., and J. Padhye, "Profile for
Datagram Congestion Control Protocol (DCCP)
Congestion Control ID 3: TCP-Friendly Rate Control
(TFRC)", RFC 4342, March 2006.
[RFC4844] Daigle, L. and Internet Architecture Board, "The
RFC Series and RFC Editor", RFC 4844, July 2007.
[RFC5237] Arkko, J. and S. Bradner, "IANA Allocation
Guidelines for the Protocol Field", BCP 37,
RFC 5237, February 2008.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)",
RFC 5389, October 2008.
[RFC5766] Mahy, R., Matthews, P., and J. Rosenberg,
"Traversal Using Relays around NAT (TURN): Relay
Extensions to Session Traversal Utilities for NAT
(STUN)", RFC 5766, April 2010.
[SRVREG] "DNS SRV Service Types Registry",
<http://www.dns-sd.org/ServiceTypes.html>.
[SYSFORM] Internet Assigned Numbers Authority (IANA),
"Application for System (Well Known) Port Number",
<http://www.iana.org/>.
[TRILOGY] "Trilogy Project",
<http://www.trilogy-project.org/>.
[USRFORM] Internet Assigned Numbers Authority (IANA),
"Application for User (Registered) Port Number",
<http://www.iana.org/>.
Cotton, et al. Best Current Practice [Page 31]
RFC 6335 Service Name and Port Number Procedures August 2011
Authors' Addresses
Michelle Cotton
Internet Corporation for Assigned Names and Numbers
4676 Admiralty Way, Suite 330
Marina del Rey, CA 90292
USA
Phone: +1 310 823 9358
EMail: michelle.cotton@icann.org
URI: http://www.iana.org/
Lars Eggert
Nokia Research Center
P.O. Box 407
Nokia Group 00045
Finland
Phone: +358 50 48 24461
EMail: lars.eggert@nokia.com
URI: http://research.nokia.com/people/lars_eggert/
Joe Touch
USC/ISI
4676 Admiralty Way
Marina del Rey, CA 90292
USA
Phone: +1 310 448 9151
EMail: touch@isi.edu
URI: http://www.isi.edu/touch
Magnus Westerlund
Ericsson
Farogatan 6
Stockholm 164 80
Sweden
Phone: +46 8 719 0000
EMail: magnus.westerlund@ericsson.com
Cotton, et al. Best Current Practice [Page 32]
RFC 6335 Service Name and Port Number Procedures August 2011
Stuart Cheshire
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
USA
Phone: +1 408 974 3207
EMail: cheshire@apple.com
URI: http://stuartcheshire.org/
Cotton, et al. Best Current Practice [Page 33]
=========================================================================
Internet Engineering Task Force (IETF) J. Touch
Request for Comments: 7605 USC/ISI
BCP: 165 August 2015
Category: Best Current Practice
ISSN: 2070-1721
Recommendations on Using Assigned Transport Port Numbers
Abstract
This document provides recommendations to designers of application
and service protocols on how to use the transport protocol port
number space and when to request a port assignment from IANA. It
provides designer guidance to requesters or users of port numbers on
how to interact with IANA using the processes defined in RFC 6335;
thus, this document complements (but does not update) that document.
It provides guidelines for designers regarding how to interact with
the IANA processes defined in RFC 6335, thus serving to complement
(but not update) that document.
Status of This Memo
This memo documents an Internet Best Current Practice.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7605.
Touch Best Current Practice [Page 1]
RFC 7605 Recommendations for Transport Port Use August 2015
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................3
2. Conventions Used in This Document ...............................3
3. History .........................................................3
4. Current Port Number Use .........................................5
5. What is a Port Number? ..........................................5
6. Conservation ....................................................7
6.1. Guiding Principles .........................................7
6.2. Firewall and NAT Considerations ............................8
7. Considerations for Requesting Port Number Assignments ...........9
7.1. Is a port number assignment necessary? .....................9
7.2. How many assigned port numbers are necessary? .............11
7.3. Picking an Assigned Port Number ...........................12
7.4. Support for Security ......................................13
7.5. Support for Future Versions ...............................14
7.6. Transport Protocols .......................................14
7.7. When to Request an Assignment .............................16
7.8. Squatting .................................................17
7.9. Other Considerations ......................................18
8. Security Considerations ........................................18
9. IANA Considerations ............................................19
10. References ....................................................19
10.1. Normative References .....................................19
10.2. Informative References ...................................20
Acknowledgments ...................................................24
Author's Address ..................................................24
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1. Introduction
This document provides information and advice to application and
service designers on the use of assigned transport port numbers. It
provides a detailed historical background of the evolution of
transport port numbers and their multiple meanings. It also provides
specific recommendations to designers on how to use assigned port
numbers. Note that this document provides information to potential
port number applicants that complements the IANA process described in
[RFC6335] (the sole document of BCP 165 before this document), but it
does not change any of the port number assignment procedures
described therein. Because they are thus so closely related, this
document and RFC 6335 are now known together as BCP 165. This
document is intended to address concerns typically raised during
Expert Review (see [RFC5226]) of assigned port number applications,
but it is not intended to bind those reviews. RFC 6335 also
describes the interaction between port experts and port requests in
IETF consensus documents. Authors of IETF consensus documents should
nevertheless follow the advice in this document and can expect
comment on their port requests from the port experts during IETF Last
Call or at other times when review is explicitly sought.
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lowercase uses of these words are not to be
interpreted as carrying significance described in RFC 2119.
In this document, the characters ">>" preceding an indented line(s)
indicates a statement using the key words listed above. This
convention aids reviewers in quickly identifying or finding
requirements for registration and recommendations for use of port
numbers in this RFC.
3. History
The term 'port' was first used in [RFC33] to indicate a simplex
communication path from an individual process and originally applied
to only the Network Control Program (NCP) connection-oriented
protocol. At a meeting described in [RFC37], an idea was presented
to decouple connections between processes and links that they use as
paths and, thus, to include numeric source and destination socket
Touch Best Current Practice [Page 3]
RFC 7605 Recommendations for Transport Port Use August 2015
identifiers in packets. [RFC38] provides further detail, describing
how processes might have more than one of these paths and that more
than one path may be active at a time. As a result, there was the
need to add a process identifier to the header of each message so
that incoming messages could be demultiplexed to the appropriate
process. [RFC38] further suggests that 32-bit numbers be used for
these identifiers. [RFC48] discusses the current notion of listening
on a specific port number, but does not discuss the issue of port
number determination. [RFC61] notes that the challenge of knowing
the appropriate port numbers is "left to the processes" in general,
but introduces the concept of a "well-known" port number for common
services.
[RFC76] proposes a "telephone book" by which an index will allow port
numbers to be used by name, but still assumes that both source and
destination port numbers are fixed by such a system. [RFC333]
proposes that a port number pair, rather than an individual port
number, be used on both sides of the connection for demultiplexing
messages. This is the final view in [RFC793] (and its predecessors,
including [IEN112]), and brings us to their current meaning.
[RFC739] introduces the notion of generic reserved port numbers for
groups of protocols, such as "any private RJE server" [RFC739].
Although the overall range of such port numbers was (and remains) 16
bits, only the first 256 (high 8 bits cleared) in the range were
considered assigned.
[RFC758] is the first to describe port numbers as being used for TCP
(previous RFCs all refer to only NCP). It includes a list of such
well-known port numbers, as well as describes ranges used for
different purposes:
Decimal Octal Description
-----------------------------------------------------------
0-63 0-77 Network Wide Standard Function
64-127 100-177 Hosts Specific Functions
128-223 200-337 Reserved for Future Use
224-255 340-377 Any Experimental Function
In [RFC820], those range meanings disappear, and a single list of
number assignments is presented. This is also the first time that
port numbers are described as applying to a connectionless transport
(e.g., UDP) rather than only connection-oriented transports.
By [RFC900], the ranges appear as decimal numbers rather than the
octal ranges used previously. [RFC1340] increases this range from
0-255 to 0-1023 and begins to list TCP and UDP port number
assignments individually (although the assumption was that once
assigned a port number applies to all transport protocols, including
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RFC 7605 Recommendations for Transport Port Use August 2015
TCP, UDP, recently Stream Control Transmission Protocol (SCTP) and
Datagram Congestion Control Protocol (DCCP), as well as ISO-TP4 for a
brief period in the early 1990s). [RFC1340] also establishes the
Registered range of 1024-59151, though it notes that it is not
controlled by the IANA (at that point). The list provided by
[RFC1700] in 1994 remained the standard until it was declared
replaced by an online version, as of [RFC3232] in 2002.
4. Current Port Number Use
RFC 6335 indicates three ranges of port number assignments:
Binary Hex
-----------------------------------------------------------
0-1023 0x0000-0x03FF System (also Well-Known)
1024-49151 0x0400-0xBFFF User (also Registered)
49152-65535 0xC000-0xFFFF Dynamic (also Private)
System (also Well-Known) encompasses the range 0-1023. On some
systems, use of these port numbers requires privileged access, e.g.,
that the process run as 'root' (i.e., as a privileged user), which is
why these are referred to as System port numbers. The port numbers
from 1024-49151 denotes non-privileged services, known as User (also
Registered), because these port numbers do not run with special
privileges. Dynamic (also Private) port numbers are not assigned.
Both System and User port numbers are assigned through IANA, so both
are sometimes called 'registered port numbers'. As a result, the
term 'registered' is ambiguous, referring either to the entire range
0-49151 or to the User port numbers. Complicating matters further,
System port numbers do not always require special (i.e., 'root')
privilege. For clarity, the remainder of this document refers to the
port number ranges as System, User, and Dynamic, to be consistent
with IANA process [RFC6335].
5. What is a Port Number?
A port number is a 16-bit number used for two distinct purposes:
o Demultiplexing transport endpoint associations within an end host
o Identifying a service
The first purpose requires that each transport endpoint association
(e.g., TCP connection or UDP pairwise association) using a given
transport between a given pair of IP addresses use a different pair
of port numbers, but it does not require either coordination or
Touch Best Current Practice [Page 5]
RFC 7605 Recommendations for Transport Port Use August 2015
registration of port number use. It is the second purpose that
drives the need for a common registry.
Consider a user wanting to run a web server. That service could run
on any port number, provided that all clients knew what port number
to use to access that service at that host. Such information can be
explicitly distributed -- for example, by putting it in the URI:
http://www.example.com:51509/
Ultimately, the correlation of a service with a port number is an
agreement between just the two endpoints of the association. A web
server can run on port number 53, which might appear as DNS traffic
to others but will connect to browsers that know to use port number
53 rather than 80.
As a concept, a service is the combination of ISO Layers 5-7 that
represents an application-protocol capability. For example, www
(port number 80) is a service that uses HTTP as an application
protocol and provides access to a web server [RFC7230]. However, it
is possible to use HTTP for other purposes, such as command and
control. This is why some current services (HTTP, e.g.) are a bit
overloaded -- they describe not only the application protocol, but a
particular service.
IANA assigns port numbers so that Internet endpoints do not need
pairwise, explicit coordination of the meaning of their port numbers.
This is the primary reason for requesting port number assignment by
IANA -- to have a common agreement between all endpoints on the
Internet as to the default meaning of a port number, which provides
the endpoints with a default port number for a particular protocol or
service.
Port numbers are sometimes used by intermediate devices on a network
path, either to monitor available services, to monitor traffic (e.g.,
to indicate the data contents), or to intercept traffic (to block,
proxy, relay, aggregate, or otherwise process it). In each case, the
intermediate device interprets traffic based on the port number. It
is important to recognize that any interpretation of port numbers --
except at the endpoints -- may be incorrect, because port numbers are
meaningful only at the endpoints. Further, port numbers may not be
visible to these intermediate devices, such as when the transport
protocol is encrypted (as in network- or link-layer tunnels) or when
a packet is fragmented (in which case only the first fragment has the
port number information). Such port number invisibility may
interfere with these capabilities, which are implemented inside the
network and based on a port number.
Touch Best Current Practice [Page 6]
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Port numbers can also be used for other purposes. Assigned port
numbers can simplify end-system configuration, so that individual
installations do not need to coordinate their use of arbitrary port
numbers. Such assignments may also have the effect of simplifying
firewall management, so that a single, fixed firewall configuration
can either permit or deny a service that uses the assigned ports.
It is useful to differentiate a port number from a service name. The
former is a numeric value that is used directly in transport protocol
headers as a demultiplexing and service identifier. The latter is
primarily a user convenience, where the default map between the two
is considered static and resolved using a cached index. This
document focuses on the former because it is the fundamental network
resource. Dynamic maps between the two, i.e., using DNS SRV records,
are discussed further in Section 7.1.
6. Conservation
Assigned port numbers are a limited resource that is globally shared
by the entire Internet community. As of 2014, approximately 5850 TCP
and 5570 UDP port numbers had been assigned out of a total range of
49151. As a result of past conservation, current assigned port use
is small and the current rate of assignment avoids the need for
transition to larger number spaces. This conservation also helps
avoid the need for IANA to rely on assigned port number reclamation,
which is practically impossible even though procedurally permitted
[RFC6335].
IANA aims to assign only one port number per service, including
variants [RFC6335], but there are other benefits to using fewer port
numbers for a given service. Use of multiple assigned port numbers
can make applications more fragile, especially when firewalls block a
subset of those port numbers or use ports numbers to route or
prioritize traffic differently. As a result:
>> Each assigned port requested MUST be justified by the applicant as
an independently useful service.
6.1. Guiding Principles
This document provides recommendations for users that also help
conserve assigned port number space. Again, this document does not
update [RFC6335] (originally the sole document of BCP 165), which
describes the IANA procedures for managing assigned transport port
numbers and services, but rather augments it by now becoming part of
BCP 165 (i.e., BCP 165 now refers to both documents together).
Assigned port number conservation is based on a number of basic
principles:
Touch Best Current Practice [Page 7]
RFC 7605 Recommendations for Transport Port Use August 2015
o A single assigned port number can support different functions over
separate endpoint associations, determined using in-band
information. An FTP data connection can transfer binary or text
files, the latter translating line-terminators, as indicated in-
band over the control port number [RFC959].
o A single assigned port number can indicate the Dynamic port
number(s) on which different capabilities are supported, as with
passive-mode FTP [RFC959].
o Several existing services can indicate the Dynamic port number(s)
on which other services are supported, such as with Multicast DNS
(mDNS) and portmapper [RFC1833] [RFC6762] [RFC6763].
o Copies of some existing services can be differentiated using in-
band information (e.g., URIs in the HTTP Host field and TLS Server
Name Indication extension) [RFC7230] [RFC6066].
o Services requiring varying performance properties can already be
supported using separate endpoint associations (connections or
other associations), each configured to support the desired
properties. For example, a high-speed and low-speed variant can
be determined within the service using the same assigned port.
Assigned port numbers are intended to differentiate services, not
variations of performance, replicas, pairwise endpoint associations,
or payload types. Assigned port numbers are also a small space
compared to other Internet number spaces; it is never appropriate to
consume assigned port numbers to conserve larger spaces such as IP
addresses, especially where copies of a service represent different
endpoints.
6.2. Firewall and NAT Considerations
Ultimately, port numbers indicate services only to the endpoints, and
any intermediate device that assigns meaning to a value can be
incorrect. End systems might agree to run web services (HTTP) over
port number 53 (typically used for DNS) rather than port number 80,
at which point a firewall that blocks port number 80 but permits port
number 53 would not have the desired effect. Nonetheless, assigned
port numbers are often used to help configure firewalls and other
port-based systems for access control.
Using Dynamic port numbers, or explicitly indicated port numbers
indicated in-band over another service (such as with FTP) often
complicates firewall and NAT interactions [RFC959]. FTP over
firewalls often requires direct support for deep-packet inspection
(to snoop for the Dynamic port number for the NAT to correctly map)
Touch Best Current Practice [Page 8]
RFC 7605 Recommendations for Transport Port Use August 2015
or passive-mode FTP (in which both connections are opened from the
client side).
7. Considerations for Requesting Port Number Assignments
Port numbers are assigned by IANA by a set of documented procedures
[RFC6335]. The following section describes the steps users can take
to help assist with responsible use of assigned port numbers and with
preparing an application for a port number assignment.
7.1. Is a port number assignment necessary?
First, it is useful to consider whether a port number assignment is
required. In many cases, a new number assignment may not be needed.
The following questions may aid in making this determination:
o Is this really a new service or could an existing service suffice?
o Is this an experimental service [RFC3692]? If so, consider using
the current experimental ports [RFC2780].
o Is this service independently useful? Some systems are composed
from collections of different service capabilities, but not all
component functions are useful as independent services. Port
numbers are typically shared among the smallest independently
useful set of functions. Different service uses or properties can
be supported in separate pairwise endpoint associations after an
initial negotiation, e.g., to support software decomposition.
o Can this service use a Dynamic port number that is coordinated
out-of-band? For example:
o By explicit configuration of both endpoints.
o By internal mechanisms within the same host (e.g., a
configuration file, indicated within a URI or using
interprocess communication).
o Using information exchanged on a related service: FTP [RFC959],
SIP [RFC3261], etc.
o Using an existing port discovery service: portmapper [RFC1833],
mDNS [RFC6762] [RFC6763], etc.
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RFC 7605 Recommendations for Transport Port Use August 2015
There are a few good examples of reasons that more directly suggest
that not only is a port number assignment not necessary, but it is
directly counter-indicated:
o Assigned port numbers are not intended to differentiate
performance variations within the same service, e.g., high-speed
versus ordinary speed. Performance variations can be supported
within a single assigned port number in context of separate
pairwise endpoint associations.
o Additional assigned port numbers are not intended to replicate an
existing service. For example, if a device is configured to use a
typical web browser, then the port number used for that service is
a copy of the http service that is already assigned to port number
80 and does not warrant a new assignment. However, an automated
system that happens to use HTTP framing -- but is not primarily
accessed by a browser -- might be a new service. A good way to
tell is to ask, "Can an unmodified client of the existing service
interact with the proposed service?". If so, that service would
be a copy of an existing service and would not merit a new
assignment.
o Assigned port numbers not intended for intra-machine
communication. Such communication can already be supported by
internal mechanisms (interprocess communication, shared memory,
shared files, etc.). When Internet communication within a host is
desired, the server can bind to a Dynamic port that is indicated
to the client using these internal mechanisms.
o Separate assigned port numbers are not intended for insecure
versions of existing (or new) secure services. A service that
already requires security would be made more vulnerable by having
the same capability accessible without security.
Note that the converse is different, i.e., it can be useful to
create a new, secure service that replicates an existing insecure
service on a new port number assignment. This can be necessary
when the existing service is not backward-compatible with security
enhancements, such as the use of TLS [RFC5246] or DTLS [RFC6347].
o Assigned port numbers are not intended for indicating different
service versions. Version differentiation should be handled in-
band, e.g., using a version number at the beginning of an
association (e.g., connection or other transaction). This may not
be possible with legacy assignments, but all new services should
incorporate support for version indication.
Touch Best Current Practice [Page 10]
RFC 7605 Recommendations for Transport Port Use August 2015
Some services may not need assigned port numbers at all, e.g., SIP
allows voice calls to use Dynamic ports [RFC3261]. Some systems can
register services in the DNS, using SRV entries. These services can
be discovered by a variety of means, including mDNS, or via direct
query [RFC6762] [RFC6763]. In such cases, users can more easily
request an SRV name, which are assigned first-come, first-served from
a much larger namespace.
IANA assigns port numbers, but this assignment is typically used only
for servers, i.e., the host that listens for incoming connections or
other associations. Clients, i.e., hosts that initiate connections
or other associations, typically refer to those assigned port numbers
but do not need port number assignments for their endpoint.
Finally, an assigned port number is not a guarantee of exclusive use.
Traffic for any service might appear on any port number, due to
misconfiguration or deliberate misuse. Application and service
designers are encouraged to validate traffic based on its content.
7.2. How many assigned port numbers are necessary?
As noted earlier, systems might require a single port number
assignment, but rarely require multiple port numbers. There are a
variety of known ways to reduce assigned port number consumption.
Although some may be cumbersome or inefficient, they are nearly
always preferable to consuming additional port number assignments.
Such techniques include:
o Use of a discovery service, either a shared service (mDNS) or a
discovery service for a given system [RFC6762] [RFC6763].
o Multiplex packet types using in-band information, either on a per-
message or per-connection basis. Such demultiplexing can even
hand off different messages and connections among different
processes, such as is done with FTP [RFC959].
There are some cases where NAT and firewall traversal are
significantly improved by having an assigned port number. Although
NAT traversal protocols supporting automatic configuration have been
proposed and developed (e.g., Session Traversal Utilities for NAT
(STUN) [RFC5389], Traversal Using Relays around NAT (TURN) [RFC5766],
and Interactive Connectivity Establishment (ICE) [RFC5245]), not all
application and service designers can rely on their presence as of
yet.
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In the past, some services were assigned multiple port numbers or
sometimes fairly large port ranges (e.g., X11). This occurred for a
variety of reasons: port number conservation was not as widely
appreciated, assignments were not as ardently reviewed, etc. This no
longer reflects current practice and such assignments are not
considered to constitute a precedent for future assignments.
7.3. Picking an Assigned Port Number
Given a demonstrated need for a port number assignment, the next
question is how to pick the desired port number. An application for
a port number assignment does not need to include a desired port
number; in that case, IANA will select from those currently
available.
Users should consider whether the requested port number is important.
For example, would an assignment be acceptable if IANA picked the
port number value? Would a TCP (or other transport protocol) port
number assignment be useful by itself? If so, a port number can be
assigned to a service for one transport protocol where it is already
(or can be subsequently) assigned to a different service for other
transport protocols.
The most critical issue in picking a number is selecting the desired
range, i.e., System versus User port numbers. The distinction was
intended to indicate a difference in privilege; originally, System
port numbers required privileged ('root') access, while User port
numbers did not. That distinction has since blurred because some
current systems do not limit access control to System port numbers
and because some System services have been replicated on User numbers
(e.g., IRC). Even so, System port number assignments have continued
at an average rate of 3-4 per year over the past 7 years (2007-2013),
indicating that the desire to keep this distinction continues.
As a result, the difference between System and User port numbers
needs to be treated with caution. Developers are advised to treat
services as if they are always run without privilege.
Even when developers seek a System port number assignment, it may be
very difficult to obtain. System port number assignment requires
IETF Review or IESG Approval and justification that both User and
Dynamic port number ranges are insufficient [RFC6335]. Thus, this
document recommends both:
>> Developers SHOULD NOT apply for System port number assignments
because the increased privilege they are intended to provide is not
always enforced.
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>> System implementers SHOULD enforce the need for privilege for
processes to listen on System port numbers.
At some future date, it might be useful to deprecate the distinction
between System and User port numbers altogether. Services typically
require elevated ('root') privileges to bind to a System port number,
but many such services go to great lengths to immediately drop those
privileges just after connection or other association establishment
to reduce the impact of an attack using their capabilities. Such
services might be more securely operated on User port numbers than on
System port numbers. Further, if System port numbers were no longer
assigned, as of 2014 it would cost only 180 of the 1024 System values
(17%), or 180 of the overall 49152 assigned (System and User) values
(<0.04%).
7.4. Support for Security
Just as a service is a way to obtain information or processing from a
host over a network, a service can also be the opening through which
to compromise that host. Protecting a service involves security,
which includes integrity protection, source authentication, privacy,
or any combination of these capabilities. Security can be provided
in a number of ways, and thus:
>> New services SHOULD support security capabilities, either directly
or via a content protection such as TLS [RFC5246] or Datagram TLS
(DTLS) [RFC6347], or transport protection such as the TCP-AO
[RFC5925]. Insecure versions of new or existing secure services
SHOULD be avoided because of the new vulnerability they create.
Secure versions of legacy services that are not already security-
capable via in-band negotiations can be very useful. However, there
is no IETF consensus on when separate ports should be used for secure
and insecure variants of the same service [RFC2595] [RFC2817]
[RFC6335]. The overall preference is for use of a single port, as
noted in Section 6 of this document and Section 7.2 of [RFC6335], but
the appropriate approach depends on the specific characteristics of
the service. As a result:
>> When requesting both secure and insecure port assignments for the
same service, justification is expected for the utility and safety of
each port as an independent service (Section 6). Precedent (e.g.,
citing other protocols that use a separate insecure port) is
inadequate justification by itself.
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It's also important to recognize that port number assignment is not
itself a guarantee that traffic using that number provides the
corresponding service or that a given service is always offered only
on its assigned port number. Port numbers are ultimately meaningful
only between endpoints and any service can be run on any port. Thus:
>> Security SHOULD NOT rely on assigned port number distinctions
alone; every service, whether secure or not, is likely to be
attacked.
Applications for a new service that requires both a secure and
insecure port may be found, on Expert Review, to be unacceptable, and
may not be approved for allocation. Similarly, an application for a
new port to support an insecure variant of an existing secure
protocol may be found unacceptable. In both cases, the resulting
security of the service in practice will be a significant
consideration in the decision as to whether to assign an insecure
port.
7.5. Support for Future Versions
Requests for assigned port numbers are expected to support multiple
versions on the same assigned port number [RFC6335]. Versions are
typically indicated in-band, either at the beginning of a connection
or other association or in each protocol message.
>> Version support SHOULD be included in new services rather than
relying on different port number assignments for different versions.
>> Version numbers SHOULD NOT be included in either the service name
or service description, to avoid the need to make additional port
number assignments for future variants of a service.
Again, the assigned port number space is far too limited to be used
as an indicator of protocol version or message type. Although this
has happened in the past (e.g., for NFS), it should be avoided in new
requests.
7.6. Transport Protocols
IANA assigns port numbers specific to one or more transport
protocols, typically UDP [RFC768] and TCP [RFC793], but also SCTP
[RFC4960], DCCP [RFC4340], and any other standard transport protocol.
Originally, IANA port number assignments were concurrent for both UDP
and TCP, and other transports were not indicated. However, to
conserve the assigned port number space and to reflect increasing use
of other transports, assignments are now specific only to the
transport being used.
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In general, a service should request assignments for multiple
transports using the same service name and description on the same
port number only when they all reflect essentially the same service.
Good examples of such use are DNS and NFS, where the difference
between the UDP and TCP services are specific to supporting each
transport. For example, the UDP variant of a service might add
sequence numbers and the TCP variant of the same service might add
in-band message delimiters. This document does not describe the
appropriate selection of a transport protocol for a service.
>> Service names and descriptions for multiple transport port number
assignments SHOULD match only when they describe the same service,
excepting only enhancements for each supported transport.
When the services differ, it may be acceptable or preferable to use
the same port number, but the service names and descriptions should
be different for each transport/service pair, reflecting the
differences in the services. For example, if TCP is used for the
basic control protocol and UDP for an alarm protocol, then the
services might be "name-ctl" and "name-alarm". A common example is
when TCP is used for a service and UDP is used to determine whether
that service is active (e.g., via a unicast, broadcast, or multicast
test message) [RFC1122]. IANA has, for several years, used the
suffix "-disc" in service names to distinguish discovery services,
such as are used to identify endpoints capable of a given service.
>> Names of discovery services SHOULD use an identifiable suffix; the
suggestion is "-disc".
Some services are used for discovery, either in conjunction with a
TCP service or as a stand-alone capability. Such services will be
more reliable when using multicast rather than broadcast (over IPv4)
because IP routers do not forward "all nodes" broadcasts (all 1's,
i.e., 255.255.255.255 for IPv4) and have not been required to support
subnet-directed broadcasts since 1999 [RFC1812] [RFC2644].
This issue is relevant only for IPv4 because IPv6 does not support
broadcast.
>> UDP over IPv4 multi-host services SHOULD use multicast rather than
broadcast.
Designers should be very careful in creating services over transports
that do not support congestion control or error recovery, notably
UDP. There are several issues that should be considered in such
cases, as summarized in Table 1 in [RFC5405]. In addition, the
following recommendations apply to service design:
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>> Services that use multipoint communication SHOULD be scalable and
SHOULD NOT rely solely on the efficiency of multicast transmission
for scalability.
>> Services SHOULD NOT use UDP as a performance enhancement over TCP,
e.g., to circumnavigate TCP's congestion control.
7.7. When to Request an Assignment
Assignments are typically requested when a user has enough
information to reasonably answer the questions in the IANA
application. IANA applications typically take up to a few weeks to
process, with some complex cases taking up to a month. The process
typically involves a few exchanges between the IANA Ports Expert
Review team and the applicant.
An application needs to include a description of the service, as well
as to address key questions designed to help IANA determine whether
the assignment is justified. The application should be complete and
not refer solely to an Internet-Draft, RFC, website, or any other
external documentation.
Services that are independently developed can be requested at any
time, but are typically best requested in the last stages of design
and initial experimentation, before any deployment has occurred that
cannot easily be updated.
>> Users MUST NOT deploy implementations that use assigned port
numbers prior their assignment by IANA.
>> Users MUST NOT deploy implementations that default to using the
experimental System port numbers (1021 and 1022 [RFC4727]) outside a
controlled environment where they can be updated with a subsequent
assigned port [RFC3692].
Deployments that use unassigned port numbers before assignment
complicate IANA management of the port number space. Keep in mind
that this recommendation protects existing assignees, users of
current services, and applicants for new assignments; it helps ensure
that a desired number and service name are available when assigned.
The list of currently unassigned numbers is just that -- *currently*
unassigned. It does not reflect pending applications. Waiting for
an official IANA assignment reduces the chance that an assignment
request will conflict with another deployed service.
Applications made through Internet-Draft posting or RFC publication
(in any stream) typically use a placeholder ("PORTNUM") in the text,
and implementations use an experimental port number until a final
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RFC 7605 Recommendations for Transport Port Use August 2015
assignment has been made [RFC6335]. That assignment is initially
indicated in the IANA Considerations section of the document, which
is tracked by the RFC Editor. When a document has been approved for
publication, that request is forwarded to IANA for handling. IANA
will make the new assignment accordingly. At that time, IANA may
also request that the applicant fill out the application form on
their website, e.g., when the RFC does not directly address the
information expected as per [RFC6335]. "Early" assignments can be
made when justified, e.g., for early interoperability testing,
according to existing process [RFC7120] [RFC6335].
>> Users writing specifications SHOULD use symbolic names for port
numbers and service names until an IANA assignment has been
completed. Implementations SHOULD use experimental port numbers
during this time, but those numbers MUST NOT be cited in
documentation except as interim.
7.8. Squatting
"Squatting" describes the use of a number from the assignable range
in deployed software without IANA assignment for that use, regardless
of whether the number has been assigned or remains available for
assignment. It is hazardous because IANA cannot track such usage and
thus cannot avoid making legitimate assignments that conflict with
such unauthorized usage.
Such "squatted" port numbers remain unassigned, and IANA retains the
right to assign them when requested by other applicants. Application
and service designers are reminded that is never appropriate to use
port numbers that have not been directly assigned [RFC6335]. In
particular, any unassigned code from the assigned ranges will be
assigned by IANA, and any conflict will be easily resolved as the
protocol designer's fault once that happens (because they would not
be the assignee). This may reflect in the public's judgment on the
quality of their expertise and cooperation with the Internet
community.
Regardless, there are numerous services that have squatted on such
numbers that are in widespread use. Designers who are using such
port numbers are encouraged to apply for an assignment. Note that
even widespread de facto use may not justify a later IANA assignment
of that value, especially if either the value has already been
assigned to a legitimate applicant or if the service would not
qualify for an assignment of its own accord.
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7.9. Other Considerations
As noted earlier, System port numbers should be used sparingly, and
it is better to avoid them altogether. This avoids the potentially
incorrect assumption that the service on such port numbers run in a
privileged mode.
Assigned port numbers are not intended to be changed; this includes
the corresponding service name. Once deployed, it can be very
difficult to recall every implementation, so the assignment should be
retained. However, in cases where the current assignee of a name or
number has reasonable knowledge of the impact on such uses, and is
willing to accept that impact, the name or number of an assignment
can be changed [RFC6335]
Aliases, or multiple service names for the same assigned port number,
are no longer considered appropriate [RFC6335].
8. Security Considerations
This document focuses on the issues arising when designing services
that require new port assignments. Section 7.4 addresses the
security and security-related issues of that interaction.
When designing a secure service, the use of TLS [RFC5246], DTLS
[RFC6347], or TCP-AO [RFC5925] mechanisms that protect transport
protocols or their contents is encouraged. It may not be possible to
use IPsec [RFC4301] in similar ways because of the different
relationship between IPsec and port numbers and because applications
may not be aware of IPsec protections.
This document reminds application and service designers that port
numbers do not protect against denial-of-service attack or guarantee
that traffic should be trusted. Using assigned numbers for port
filtering isn't a substitute for authentication, encryption, and
integrity protection. The port number alone should not be used to
avoid denial-of-service attacks or to manage firewall traffic because
the use of port numbers is not regulated or validated.
The use of assigned port numbers is the antithesis of privacy because
they are intended to explicitly indicate the desired application or
service. Strictly, port numbers are meaningful only at the
endpoints, so any interpretation elsewhere in the network can be
arbitrarily incorrect. However, those numbers can also expose
information about available services on a given host. This
information can be used by intermediate devices to monitor and
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intercept traffic as well as to potentially identify key endpoint
software properties ("fingerprinting"), which can be used to direct
other attacks.
9. IANA Considerations
The entirety of this document focuses on suggestions that help ensure
the conservation of port numbers and provide useful hints for issuing
informative requests thereof.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
Values In the Internet Protocol and Related Headers", BCP
37, RFC 2780, DOI 10.17487/RFC2780, March 2000,
<http://www.rfc-editor.org/info/rfc2780>.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692,
DOI 10.17487/RFC3692, January 2004,
<http://www.rfc-editor.org/info/rfc3692>.
[RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4,
ICMPv6, UDP, and TCP Headers", RFC 4727,
DOI 10.17487/RFC4727, November 2006,
<http://www.rfc-editor.org/info/rfc4727>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
for Application Designers", BCP 145, RFC 5405,
DOI 10.17487/RFC5405, November 2008,
<http://www.rfc-editor.org/info/rfc5405>.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <http://www.rfc-editor.org/info/rfc5925>.
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RFC 7605 Recommendations for Transport Port Use August 2015
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165, RFC
6335, DOI 10.17487/RFC6335, August 2011,
<http://www.rfc-editor.org/info/rfc6335>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>.
10.2. Informative References
[IEN112] Postel, J., "Transmission Control Protocol", IEN 112,
August 1979.
[RFC33] Crocker, S., "New Host-Host Protocol", RFC 33,
DOI 10.17487/RFC0033, February 1970,
<http://www.rfc-editor.org/info/rfc33>.
[RFC37] Crocker, S., "Network Meeting Epilogue, etc", RFC 37,
DOI 10.17487/RFC0037, March 1970,
<http://www.rfc-editor.org/info/rfc37>.
[RFC38] Wolfe, S., "Comments on Network Protocol from NWG/RFC
#36", RFC 38, DOI 10.17487/RFC0038, March 1970,
<http://www.rfc-editor.org/info/rfc38>.
[RFC48] Postel, J. and S. Crocker, "Possible protocol plateau",
RFC 48, DOI 10.17487/RFC0048, April 1970,
<http://www.rfc-editor.org/info/rfc48>.
[RFC61] Walden, D., "Note on Interprocess Communication in a
Resource Sharing Computer Network", RFC 61,
DOI 10.17487/RFC0061, July 1970,
<http://www.rfc-editor.org/info/rfc61>.
[RFC76] Bouknight, J., Madden, J., and G. Grossman, "Connection by
name: User oriented protocol", RFC 76,
DOI 10.17487/RFC0076, October 1970,
<http://www.rfc-editor.org/info/rfc76>.
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[RFC333] Bressler, R., Murphy, D., and D. Walden, "Proposed
experiment with a Message Switching Protocol", RFC 333,
DOI 10.17487/RFC0333, May 1972,
<http://www.rfc-editor.org/info/rfc333>.
[RFC739] Postel, J., "Assigned numbers", RFC 739,
DOI 10.17487/RFC0739, November 1977,
<http://www.rfc-editor.org/info/rfc739>.
[RFC758] Postel, J., "Assigned numbers", RFC 758,
DOI 10.17487/RFC0758, August 1979,
<http://www.rfc-editor.org/info/rfc758>.
[RFC768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<http://www.rfc-editor.org/info/rfc768>.
[RFC793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>.
[RFC820] Postel, J., "Assigned numbers", RFC 820,
DOI 10.17487/RFC0820, August 1982,
<http://www.rfc-editor.org/info/rfc820>.
[RFC900] Reynolds, J. and J. Postel, "Assigned Numbers", RFC 900,
DOI 10.17487/RFC0900, June 1984,
<http://www.rfc-editor.org/info/rfc900>.
[RFC959] Postel, J. and J. Reynolds, "File Transfer Protocol", STD
9, RFC 959, DOI 10.17487/RFC0959, October 1985,
<http://www.rfc-editor.org/info/rfc959>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<http://www.rfc-editor.org/info/rfc1122>.
[RFC1340] Reynolds, J. and J. Postel, "Assigned Numbers", RFC 1340,
DOI 10.17487/RFC1340, July 1992,
<http://www.rfc-editor.org/info/rfc1340>.
[RFC1700] Reynolds, J. and J. Postel, "Assigned Numbers", RFC 1700,
DOI 10.17487/RFC1700, October 1994,
<http://www.rfc-editor.org/info/rfc1700>.
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[RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers",
RFC 1812, DOI 10.17487/RFC1812, June 1995,
<http://www.rfc-editor.org/info/rfc1812>.
[RFC1833] Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
RFC 1833, DOI 10.17487/RFC1833, August 1995,
<http://www.rfc-editor.org/info/rfc1833>.
[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC
2595, DOI 10.17487/RFC2595, June 1999,
<http://www.rfc-editor.org/info/rfc2595>.
[RFC2644] Senie, D., "Changing the Default for Directed Broadcasts
in Routers", BCP 34, RFC 2644, DOI 10.17487/RFC2644,
August 1999, <http://www.rfc-editor.org/info/rfc2644>.
[RFC2817] Khare, R. and S. Lawrence, "Upgrading to TLS Within
HTTP/1.1", RFC 2817, DOI 10.17487/RFC2817, May 2000,
<http://www.rfc-editor.org/info/rfc2817>.
[RFC3232] Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is Replaced
by an On-line Database", RFC 3232, DOI 10.17487/RFC3232,
January 2002, <http://www.rfc-editor.org/info/rfc3232>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <http://www.rfc-editor.org/info/rfc4301>.
[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", RFC 4340,
DOI 10.17487/RFC4340, March 2006,
<http://www.rfc-editor.org/info/rfc4340>.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<http://www.rfc-editor.org/info/rfc4960>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
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[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
DOI 10.17487/RFC5245, April 2010,
<http://www.rfc-editor.org/info/rfc5245>.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
DOI 10.17487/RFC5389, October 2008,
<http://www.rfc-editor.org/info/rfc5389>.
[RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)", RFC 5766,
DOI 10.17487/RFC5766, April 2010,
<http://www.rfc-editor.org/info/rfc5766>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<http://www.rfc-editor.org/info/rfc6066>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<http://www.rfc-editor.org/info/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<http://www.rfc-editor.org/info/rfc6763>.
[RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code
Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
2014, <http://www.rfc-editor.org/info/rfc7120>.
[RFC7230] Fielding, R., Ed., and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
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Acknowledgments
This work benefited from the feedback from David Black, Lars Eggert,
Gorry Fairhurst, and Eliot Lear, as well as discussions of the IETF
TSVWG WG.
This document was initially prepared using 2-Word-v2.0.template.dot.
Author's Address
Joe Touch
USC/ISI
4676 Admiralty Way
Marina del Rey, CA 90292-6695
United States
Phone: +1 (310) 448-9151
Email: touch@isi.edu
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