Internet DRAFT - draft-steinberg-6man-crh-vs-sr-mpls
draft-steinberg-6man-crh-vs-sr-mpls
6MAN D. Steinberg, Ed.
Internet-Draft Lapishills Consulting Limited
Intended status: Informational W. Henderickx
Expires: December 31, 2020 Nokia
Z. Li
Huawei Technologies
W. Cheng
China Mobile
D. Voyer
Bell Canada
June 29, 2020
SR-MPLS over IPv6 satisfies CRH requirements
draft-steinberg-6man-crh-vs-sr-mpls-00
Abstract
SR-MPLS is a mature solution that provides highly scalable traffic
engineering capabilities in MPLS networks. This document analyzes
how SR-MPLS over IP exceeds the capabilities of the CRH, making the
latter redundant.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. A Label by any Other Name . . . . . . . . . . . . . . . . . . 2
3. An Endpoint is an Endpoint . . . . . . . . . . . . . . . . . 3
4. All Roads Lead to Rome . . . . . . . . . . . . . . . . . . . 3
5. You Can't Manage What You Can't Measure . . . . . . . . . . . 3
6. MTU Overhead . . . . . . . . . . . . . . . . . . . . . . . . 3
7. Services . . . . . . . . . . . . . . . . . . . . . . . . . . 4
8. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 4
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
9.1. Normative References . . . . . . . . . . . . . . . . . . 4
9.2. Informative References . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
SR-MPLS [RFC8660] is a mature solution that provides highly scalable
traffic engineering capabilities in MPLS networks.
By encapsulating the MPLS label stack in an IPv4 or IPv6 [RFC4023],
or IP+UDP [RFC7510] header, an SR-MPLS policy can seamlessly traverse
IP-only routers in a network [RFC8663].
The SR-MPLS control plane can run on top of IPv4 or IPv6. The latter
is reminded in [I-D.filsfils-spring-sr-mpls-ipv6-control-plane].
This document analyzes how SR-MPLS over IP provides all the
capabilities of CRH [I-D.bonica-6man-comp-rtg-hdr], making CRH
redundant.
The analysis shows that the capabilities provided by CRH are in fact
a subset of the capabilities provided by SR-MPLS over IPv6.
2. A Label by any Other Name
[I-D.bonica-6man-comp-rtg-hdr] specifies the encoding of identifiers
in 16- or 32-bit values and places them in the CRH. The CRH is to be
inspected at each node represented by an identifier.
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SR-MPLS over IP encodes identifiers in 20-bit values within 32 bit
labels and places them in an in the SR-MPLS or UDP header.
Because these encodings must translate into an action and a location
(IPv6 address) there is really no difference between these encodings,
in the end a 32-bit label is just a label that can identify anything
at an endpoint.
3. An Endpoint is an Endpoint
A node transmitting a packet containing a set of identifiers placed
within a CRH writes the IPv6 address of the first segment endpoint
into the destination address of the IPv6 header.
The same is true for SR-MPLS over IP, the source node writes the IPv6
address of the first segment endpoint into the destination address of
the IPv6 header.
There is no functional difference between the SR-MPLS over IP
endpoint vs the CRH endpoint, both receive a packet destined to their
interface and process the next segment.
4. All Roads Lead to Rome
At a segment endpoint the router receives the packet destined to it,
processes the next segment (MPLS label or CRH segment ID) and
rewrites the outer IPv6 header with a new destination address. The
CRH calls this table that maps labels to behavior and a destination
address a SFIB, however this is identical to the SR-MPLS label table.
Ultimately, the packet is received at the final destination within
the domain and the packets payload is processed. All roads do indeed
lead to Rome.
5. You Can't Manage What You Can't Measure
IP ping and traceroute just work for either SR-MPLS over IP or CRH.
SR-MPLS has a rich set of OAM mechanisms ([RFC8287]), and these
mechanisms are available for SR-MPLS over IP deployments.
CRH has no OAM defined for its labels.
6. MTU Overhead
Both SR-MPLS over IPv6 and CRH require an IPv6 header. However, due
to the overhead required for extension headers, CRH always results in
greater overhead in its 32 bit flavor vs SR-MPLS over IP. For the
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CRH 16 bit flavor, SR-MPLS over IP still has a lower overhead for up
to 5 labels.
7. Services
MPLS has a rich set of services that are defined and translate into
MPLS labels. Protocols and SDN mechanisms to distribute these
service labelse are well known.
CRH has no service support, it is simply a transport header carrying
transport identifiers. It relies on other headers and identifiers to
provide services.
8. Conclusion
This analysis shows that CRH and the identifiers it carries do not
provide any demonstrable benefit beyond what SR-MPLS over IPv6
provides, in fact it can only support a subset of what SR-MPLS over
IPv6 is capable of. Furthermore, OAM is fully defined for SR-MPLS
and the control planes supporting SR-MPLS are mature and well
defined.
The conclusion is that there is no value in defining another header
to map labels to behaviors and IPv6 addresses within a domain. This
exists and it is SR-MPLS over IPv6.
9. References
9.1. Normative References
[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
[RFC8663] Xu, X., Bryant, S., Farrel, A., Hassan, S., Henderickx,
W., and Z. Li, "MPLS Segment Routing over IP", RFC 8663,
DOI 10.17487/RFC8663, December 2019,
<https://www.rfc-editor.org/info/rfc8663>.
9.2. Informative References
[I-D.bonica-6man-comp-rtg-hdr]
Bonica, R., Kamite, Y., Niwa, T., Alston, A., and L.
Jalil, "The IPv6 Compact Routing Header (CRH)", draft-
bonica-6man-comp-rtg-hdr-22 (work in progress), May 2020.
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[I-D.filsfils-spring-sr-mpls-ipv6-control-plane]
Filsfils, C., Clad, F., and K. Talaulikar, "SR-MPLS Data
Plane with IPv6 Control Plane", draft-filsfils-spring-sr-
mpls-ipv6-control-plane-02 (work in progress), May 2020.
[RFC4023] Worster, T., Rekhter, Y., and E. Rosen, Ed.,
"Encapsulating MPLS in IP or Generic Routing Encapsulation
(GRE)", RFC 4023, DOI 10.17487/RFC4023, March 2005,
<https://www.rfc-editor.org/info/rfc4023>.
[RFC7510] Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
"Encapsulating MPLS in UDP", RFC 7510,
DOI 10.17487/RFC7510, April 2015,
<https://www.rfc-editor.org/info/rfc7510>.
[RFC8287] Kumar, N., Ed., Pignataro, C., Ed., Swallow, G., Akiya,
N., Kini, S., and M. Chen, "Label Switched Path (LSP)
Ping/Traceroute for Segment Routing (SR) IGP-Prefix and
IGP-Adjacency Segment Identifiers (SIDs) with MPLS Data
Planes", RFC 8287, DOI 10.17487/RFC8287, December 2017,
<https://www.rfc-editor.org/info/rfc8287>.
Authors' Addresses
Dirk Steinberg (editor)
Lapishills Consulting Limited
Cyprus
Email: dirk@lapishills.com
Wim Henderickx
Nokia
Belgium
Email: wim.henderickx@nokia.com
Zhenbin Li
Huawei Technologies
China
Email: lizhenbin@huawei.com
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Weiqiang Cheng
China Mobile
China
Email: chengweiqiang@chinamobile.com
Daniel Voyer
Bell Canada
Canada
Email: daniel.voyer@bell.ca
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