Rob,
There may be an elephant in the room that needs addressing....
Over the years, the IPv6 community has specified a very tight architecture that
encodes some information in IPv6 addresses, other information in Routing
headers, and still other information in Destination Options headers. SRv6+
adheres strictly to this architecture. Because it reuses IPv6 machinery, its
specification promises it be painless and its deployment promises to be safe.
To date, there has been no significant technical criticism of SRv6+.. Only a
claim that SRv6 is nearly complete and good enough. (Both of those claims may
require scrutiny).
By contrast, SRv6 varies from the spirit, if not the letter of the IPv6
architecture. It encodes things in IPv6 address that have never been encoded in
IPv6 addresses before. It attempts to encode everything else in the Routing
header, as if the other IPv6 extension headers didn't exist. It frequently
tests the limits of RFC 8200 compliance.
This creates a situation in which each variance from IPv6 orthodoxy requires
another. For example, because SRv6 encodes instructions in IPv6 addresses,
draft-ali-6man-spring-srv6-oam is required. And now,
draft-ali-6man-spring-srv6-oam creates its own variances from the IPv6
orthodoxy. OAM information is encoded in the Routing header and the Routing
header must be examined, even when Segment Left is equal to zero.
I invite everyone to consider how TI-LFA an uSID will interact.
So, why would the IETF would want to prevent work on the more conservative,
SRv6+ approach? This brings us to the back to the elephant in the room......
Until very recently, relatively few router vendors have supported IPv6
extension headers in ASICs. If an IPv6 packet contained any extension headers
at all, it was sent to the slow path.
SRv6+ encourages router vendors to support both the Routing and Destination
Options header in ASICs. This sets vendors on a path on a path towards more
complete implementation of the architecture that the IPv6 community has
developed so carefully over the years. It encourages vendors to commit more and
more of RFC 8200 to ASICs.
SRv6 encourages router vendors to support the Routing header in ASICs, while
doing everything possible to mitigate the need to support Destination Options
in ASICs. This may be a necessary expedient for many platforms. However, it
should not be the only approach, or even the long-term approach for the IETF.
Ron
From: spring <spring-boun...@ietf.org> On Behalf Of Rob Shakir
Sent: Sunday, August 4, 2019 5:04 PM
To: SPRING WG List <spring@ietf.org>
Subject: [spring] Beyond SRv6.
Hi SPRING WG,
Over the last 5+ years, the IETF has developed Source Packet Routing in
NetworkinG (SPRING) aka Segment Routing for both the MPLS (SR-MPLS) and IPv6
(SRv6) data planes. SR-MPLS may also be transported over IP in UDP or GRE.
These encapsulations are past WG last call (in IESG or RFC Editor).
During the SPRING WG meeting at IETF 105, two presentations were related to the
reduction of the size of the SID for IPv6 dataplane:
* SRv6+ / CRH --
https://tools.ietf.org/html/draft-bonica-spring-srv6-plus-04<https://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org_html_draft-2Dbonica-2Dspring-2Dsrv6-2Dplus-2D04&d=DwMFaQ&c=HAkYuh63rsuhr6Scbfh0UjBXeMK-ndb3voDTXcWzoCI&r=Fch9FQ82sir-BoLx84hKuKwl-AWF2EfpHcAwrDThKP8&m=ackZC9evRf_LWYu2a-1NaGRDJKdxnE2ieIC4dD_FL6s&s=KUhAfjVsx_wK645uJk0FHzs2vxiAVr-CskMPAaEhEQQ&e=>
* uSID --
https://tools.ietf.org/html/draft-filsfils-spring-net-pgm-extension-srv6-usid-01<https://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org_html_draft-2Dfilsfils-2Dspring-2Dnet-2Dpgm-2Dextension-2Dsrv6-2Dusid-2D01&d=DwMFaQ&c=HAkYuh63rsuhr6Scbfh0UjBXeMK-ndb3voDTXcWzoCI&r=Fch9FQ82sir-BoLx84hKuKwl-AWF2EfpHcAwrDThKP8&m=ackZC9evRf_LWYu2a-1NaGRDJKdxnE2ieIC4dD_FL6s&s=Aq1DK7fu73axZ1PXLIE8xnHE2AhTtNZy9LTHgWqx4CQ&e=>
During the IETF week, two additional drafts have been proposed:
*
https://tools.ietf.org/html/draft-li-spring-compressed-srv6-np-00<https://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org_html_draft-2Dli-2Dspring-2Dcompressed-2Dsrv6-2Dnp-2D00&d=DwMFaQ&c=HAkYuh63rsuhr6Scbfh0UjBXeMK-ndb3voDTXcWzoCI&r=Fch9FQ82sir-BoLx84hKuKwl-AWF2EfpHcAwrDThKP8&m=ackZC9evRf_LWYu2a-1NaGRDJKdxnE2ieIC4dD_FL6s&s=XWUDAD2FMhWLfeT5sgUb1lgthJhugcyT98GJ2N-CrKs&e=>
*
https://tools.ietf.org/html/draft-mirsky-6man-unified-id-sr-03<https://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org_html_draft-2Dmirsky-2D6man-2Dunified-2Did-2Dsr-2D03&d=DwMFaQ&c=HAkYuh63rsuhr6Scbfh0UjBXeMK-ndb3voDTXcWzoCI&r=Fch9FQ82sir-BoLx84hKuKwl-AWF2EfpHcAwrDThKP8&m=ackZC9evRf_LWYu2a-1NaGRDJKdxnE2ieIC4dD_FL6s&s=gcbkHYxXm7FU7vblOB1vI58SDaaWf62pa7YvLmsP4nI&e=>
As we expressed during the meeting, it is important for the WG to understand
what the aims of additional encapsulations are. Thus, we think it is important
that the WG should first get to a common understanding on the requirements for
a new IPv6 data plane with a smaller SID - both from the perspective of
operators that are looking to deploy these technologies, and from that of the
software/hardware implementation.
Therefore, we would like to solicit network operators interested in SR over the
IPv6 data plane to briefly introduce their:
* use case (e.g. Fast Reroute, explicit routing/TE)
* forwarding performance and scaling requirements
* e.g., (number of nodes, network diameter, number of SID required in
max and average). For the latter, if possible using both SRv6 128-bit SIDs and
shorter (e.g. 32-bit) SIDs as the number would typically be different (*).
* if the existing SRv6 approach is not deployable in their circumstances,
details of the requirement of a different solution is required and whether this
solution is needed for the short term only or for the long term.
As well as deployment limitations, we would like the SPRING community to
briefly describe the platform limitations that they are seeing which limit the
deployment of SRv6 In particular limitations related to the number of SIDs
which can be pushed and forwarded and how much the use of shorter SIDs would
improve the deployments .
For both of these sets of feedback if possible, please post this to the SPRING
WG. If the information cannot be shared publicly, please send it directly to
the chairs & AD (Martin).
This call for information will run for four weeks, up to 2019/09/03. As a
reminder, you can reach the SPRING chairs via
spring-cha...@ietf.org<mailto:spring-cha...@ietf.org> and ADs via
spring-...@ietf.org<mailto:spring-...@ietf.org>.
Thank you,
-- Rob & Bruno
(*) As expressed on the mailing list, a 128 bit SID can encode two instructions
a node SID and an adjacency SID hence less SID may be required.
Juniper Business Use Only
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