Internet Engineering Task Force (IETF) J. Brzozowski
Request for Comments: 8354 J. Leddy
Category: Informational Comcast
ISSN: 2070-1721 C. Filsfils
R. Maglione, Ed.
M. Townsley
Cisco Systems
March 2018
Use Cases for IPv6 Source Packet Routing in Networking (SPRING)
Abstract
The Source Packet Routing in Networking (SPRING) architecture
describes how Segment Routing can be used to steer packets through an
IPv6 or MPLS network using the source routing paradigm. This
document illustrates some use cases for Segment Routing in an
IPv6-only environment.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
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). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8354.
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Copyright Notice
Copyright (c) 2018 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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. IPv6 SPRING Use Cases . . . . . . . . . . . . . . . . . . . . 3
2.1. SPRING in the Small Office . . . . . . . . . . . . . . . 3
2.2. SPRING in the Access Network . . . . . . . . . . . . . . 4
2.3. SPRING in Data Center . . . . . . . . . . . . . . . . . . 5
2.4. SPRING in Content Delivery Networks . . . . . . . . . . . 5
2.5. SPRING in Core Networks . . . . . . . . . . . . . . . . . 6
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Normative References . . . . . . . . . . . . . . . . . . 7
5.2. Informative References . . . . . . . . . . . . . . . . . 7
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
Source Packet Routing in Networking (SPRING) architecture leverages
the source routing paradigm. An ingress node steers a packet by
including a controlled set of instructions, called segments, in the
SPRING header. The SPRING architecture is described in
[SEGMENT-ROUTING]. This document illustrates some use cases for
SPRING / Segment Routing in an IPv6-only environment.
2. IPv6 SPRING Use Cases
The use cases described in this section do not constitute an
exhaustive list of all the possible scenarios: this section only
includes some of the most common envisioned deployment models for
Segment Routing over IPv6 (SRv6).
In addition to the use cases described in this document, all the
SPRING use cases [RFC7855] are also applicable to the SRv6 data
plane.
2.1. SPRING in the Small Office
An IPv6-enabled Small Office, Home Office (SOHO) provides ample
globally routed IP addresses for all devices in the SOHO. An IPv6
small office with multiple egress points and associated provider-
assigned prefixes will, in turn, provide multiple IPv6 addresses to
hosts. A small office performing source and destination routing
[PA-MULTIHOMING] will ensure that packets exit the SOHO at the
appropriate egress based on the associated delegated prefix for that
link.
A SPRING-enabled SOHO provides the ability to steer traffic into a
specific path from end hosts in the SOHO or from a customer edge
router in the SOHO. If the selection of the source-routed path is
enabled at the customer edge router, that router is responsible for
classifying traffic and steering it into the correct path. If hosts
in the SOHO have explicit source selection rules, classification can
be based on the source address or associated network egress point,
thus avoiding the need for implicit classification techniques based
on Deep Packet Inspection (DPI). If the traffic is steered into a
specific path by the host itself, it is important to know which
networks can interpret the SPRING header. This information can be
provided as part of the host configuration as a property of the
configured IP address.
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The ability to steer traffic to an appropriate egress or utilize a
specific type of media (e.g., low power, Wi-Fi, wired, femtocell,
Bluetooth, Multimedia over Coax Alliance (MoCA), HomePlug, etc.)
within the home itself are obvious cases that may be of interest to
an application running within a SOHO.
Steering to a specific egress point may be useful for a number of
scenarios, including:
o regulatory compliance;
o performance of a particular service associated with a particular
link;
o cost imposed due to data caps or per-byte charges;
o distinguishing between personal vs. work traffic in homes with one
or more teleworkers; and
o provision of specific services by one ISP vs. another.
Information included in the SPRING header, whether imposed by the end
host itself, a customer edge router, or within the access network of
the ISP, may be of use at the far ends of the data communication as
well. For example, an application running on an end host with
application support in a data center can utilize the SPRING header as
a channel to include information that affects its treatment within
the data center itself, which allows for application-level steering
and load balancing without relying upon implicit application-
classification techniques at the edge of the data center. Further,
as more and more application traffic is encrypted, the ability to
extract (and include in the SPRING header) just enough information to
enable the network and data center to load balance and steer traffic
appropriately becomes more and more important.
2.2. SPRING in the Access Network
Access networks deliver a variety of types of traffic from the
service provider's network to the home environment and from the home
towards the service provider's network.
For bandwidth management or related purposes, the service provider
may want to associate certain types of traffic to specific physical
or logical downstream capacity pipes.
This mapping is not the same thing as classification and scheduling.
In the cable access network, these pipes are represented at the Data-
Over-Cable Service Interface Specification [DOCSIS] layer as
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different service flows, which are better identified as distinct data
links. As such, creating this separation allows an operator to
differentiate between different types of content and perform a
variety of differing functions on these pipes, such as byte capping,
regulatory compliance functions, and billing.
In a cable operator's environment, these downstream pipes could be a
DOCSIS [DOCSIS] service flow, a service group, or a specific
Quadrature Amplitude Modulation (QAM) as in Annex B of [ITU.J83].
Similarly, the operator may want to map traffic from the home sent
towards the service provider's network to specific upstream capacity
pipes. Information carried in a packet's SPRING header could provide
the target pipe for this specific packet. The access device would
not need to know specific details about the packet to perform this
mapping; instead, the access device would only need to know the
interpretation of the SPRING header and how to map it to the target
pipe.
2.3. SPRING in Data Center
Some data center operators are transitioning their data center
infrastructure from IPv4 to native IPv6 only, in order to cope with
IPv4 address depletion and to achieve larger scale. In such an
environment, source routing (as enabled by SRv6) can be used to steer
traffic across specific paths through the network. The specific path
may also include a given function that one or more nodes in the path
are requested to perform.
Additionally, one of the fundamental requirements for data center
architecture is to provide scalable, isolated tenant networks. In
such scenarios, Segment Routing can be used to build a construct to
steer the traffic across that specific path and to identify specific
nodes, tenants, and functions.
2.4. SPRING in Content Delivery Networks
The rise of online video applications and new, video-capable IP
devices has led to an explosion of video traffic traversing network
operator infrastructures. In the drive to reduce the capital and
operational impact of the massive influx of online video traffic, as
well as to extend traditional TV services to new devices and screens,
network operators are increasingly turning to Content Delivery
Networks (CDNs).
Several studies showed the benefits of connecting caches in a
hierarchical structure following the hierarchical nature of the
Internet. In a cache hierarchy, one cache establishes peering
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relationships with its neighbor caches. There are two types of
relationships: parent and sibling. A parent cache is essentially one
level up in a cache hierarchy. A sibling cache is on the same level.
Multiple levels of hierarchy are commonly used in order to build an
efficient cache architecture.
In an environment where each single cache system can be uniquely
identified by its own IPv6 address, a list containing a sequence of
the caches in a hierarchy can be built. At each node (cache) in the
list, the presence of the requested content is checked. If the
requested content is found at the cache (a cache hits scenario), the
sequence ends even if there are more nodes in the list; otherwise,
the next element in the list (the next node/cache) is examined.
2.5. SPRING in Core Networks
While the overall amount of traffic offered to the network continues
to grow, and considering that multiple types of traffic with
different characteristics and requirements are quickly converging
over a single network architecture, the network operators are
starting to face new challenges.
Some operators are currently building, or plan to build in the near
future, an IPv6-only native infrastructure for their core network.
These operators are also looking at the possibility to set up an
explicit path based on the IPv6 source address for specific types of
traffic in order to efficiently use their network infrastructure. In
the case of IPv6, some operators are currently assigning or plan to
assign IPv6 prefix(es) to their IPv6 customers based on regions/
geography, thus the subscriber's IPv6 prefix could be used to
identify the region where the customer is located. In such an
environment, the IPv6 source address could be used by the edge nodes
of the network to steer traffic and forward it through a specific
path other than the optimal path.
The need to set up a source-based path that goes through some
specific middle/intermediate points in the network may be related to
different requirements:
o The operator may want to be able to use some high-bandwidth links
for a specific type of traffic (like video) and thus avoid the
need for overdimensioning all the links of the network;
o The operator may want to be able to set up a specific path for
delay-sensitive applications;
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o The operator may have the need to be able to select one (or
multiple) specific exit point(s) at peering points when different
peering points are available;
o The operator may have the need to be able to set up a source-based
path for specific services in order to be able to reach some
servers hosted in some facilities that are not always reachable
through the optimal path; or
o The operator may need to be able to provision guaranteed disjoint
paths (a so-called "dual-plane network") for diversity purposes.
All these scenarios would require a form of traffic engineering
capabilities in an IPv6-only network environment.
3. IANA Considerations
This document has no IANA actions.
4. Security Considerations
This document presents use cases to be considered by the SPRING
architecture and potential IPv6 extensions. As such, it does not
introduce any security considerations. However, there are a number
of security concerns with source routing at the IP layer [RFC5095].
It is expected that any solution that addresses these use cases also
addresses any security concerns.
5. References
5.1. Normative References
[RFC7855] Previdi, S., Ed., Filsfils, C., Ed., Decraene, B.,
Litkowski, S., Horneffer, M., and R. Shakir, "Source
Packet Routing in Networking (SPRING) Problem Statement
and Requirements", RFC 7855, DOI 10.17487/RFC7855,
May 2016, <https://www.rfc-editor.org/info/rfc7855>.
5.2. Informative References
[DOCSIS] CableLabs, "New Generation of DOCSIS Technology", October
2013, <http://www.cablelabs.com/news/
new-generation-of-docsis-technology/>.
[ITU.J83] ITU-T, "Digital multi-programme systems for television,
sound and data services or cable distribution", ITU-T
Recommendation J.83, December 2007,
<https://www.itu.int/rec/T-REC-J.83/en>.
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[PA-MULTIHOMING]
Baker, F., Bowers, C., and J. Linkova, "Enterprise
Multihoming using Provider-Assigned Addresses without
Network Prefix Translation: Requirements and Solution",
Work in Progress, draft-ietf-rtgwg-enterprise-pa-
multihoming-03, February 2018.
[RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
of Type 0 Routing Headers in IPv6", RFC 5095,
DOI 10.17487/RFC5095, December 2007,
<https://www.rfc-editor.org/info/rfc5095>.
[SEGMENT-ROUTING]
Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing
Architecture", Work in Progress, draft-ietf-spring-
segment-routing-15, January 2018.
Acknowledgements
The authors would like to thank Brian Field, Robert Raszuk, Wes
George, Eric Vyncke, Fred Baker, John G. Scudder, Adrian Farrel,
Alvaro Retana, Bruno Decraene, and Yakov Rekhter for their valuable
comments and inputs to this document.
Contributors
Many people contributed to this document. The authors of this
document would like to thank and recognize them and their
contributions. These contributors provided invaluable concepts and
content for this document's creation.
Ida Leung
Independent
Email: ida@brumund.ca
Stefano Previdi
Cisco Systems
Via Del Serafico, 200
Rome 00142
Italy
Email: stefano@previdi.net
Christian Martin
Arista Networks
Email: cmartin@arista.com
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Authors' Addresses
John Brzozowski
Comcast
Email: john_brzozowski@cable.comcast.com
John Leddy
Comcast
Email: John_Leddy@cable.comcast.com
Clarence Filsfils
Cisco Systems
Brussels
Belgium
Email: cfilsfil@cisco.com
Roberta Maglione (editor)
Cisco Systems
Via Torri Bianche 8
Vimercate 20871
Italy
Email: robmgl@cisco.com
Mark Townsley
Cisco Systems
Email: townsley@cisco.com
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