Robert,
I can only repeat what my customers' requirements. They have asked for 8-12
SIDs in SR-MPLS and SRv6 and SRv6+.
We didn't question that requirement for SR-MPLS. Why should things be any
different for SRv6 or SRv6+?
Ron
From: Robert Raszuk <rob...@raszuk.net>
Sent: Sunday, September 1, 2019 11:03 AM
To: Ron Bonica <rbon...@juniper.net>
Cc: Rob Shakir <ro...@google.com>; SPRING WG List <spring@ietf.org>;
6...@ietf.org
Subject: Re: [spring] Beyond SRv6.
Dear Ron,
> SR customers have stated a firm requirement to support SR paths that contain
> 8 to 12 segments.
Let me make an observation that with 8 to 12 router hops I can reach most of my
often visited destinations in the open Internet anywhere in the world.
With that let's also notice that proposed SRv6 (or for that matter SR-MPLS) is
applicable to networks under same administrative control.
Therefor I do question the necessity to have such deep/long list of segments
for any practical network application.
Perhaps some customers (or vendors) are treating SRv6 verbatim as an analogy to
RSVP-TE strict or loose ERO objects - but that is completely wrong way to think
about it in light of segment routing architecture and its abilities.
In RSVP-TE you nail down the path with hop by hop RESV-PATH msg signalling such
that forwarding is using locally upstream assigned labels distributed by return
RSVP-RESV msg.
I would never suggest to do same with SR. The biggest advantage of SR (outside
of its network programmability concept) is in the ability to encode very
selected anchor node or nodes to which forwarding just flows natively using
IPv6 address or domain wide MPLS label.
So proper use of SR does require wise selection of such anchor points in the
network. I am afraid CSPF is not the best tool for it. Much smarter algorithm
is required to engineer your traffic using SR technology in any network
especially in cases where the IGP topology is very dense and complex.
Based on my personal experience with MPLS-TE deployments across biggest global
networks I can state that vast majority of true path steering can be easily
accomplished with 1, 2 or max 3 properly selected anchor nodes across their
domain(s). Add to that room for two SFC processing clusters and you get max 5.
So even if some individual operators would like to use 8, 12 or maybe 16
segments in their packets I do not see this as fundamentally sufficient
justification to proceed with yet one more SRv6 encoding proposal.
As both Rob & Bruno asked I will be looking for real technical justifications
for such deep segment stacks. Note that we are at the end of 4 week pool window
and there was none sent to the list so far.
Kind regards,
Robert.
On Sat, Aug 31, 2019 at 10:34 PM Ron Bonica
<rbonica=40juniper....@dmarc.ietf.org<mailto:40juniper....@dmarc.ietf.org>>
wrote:
Rob,
The following are arguments for proceeding with SRv6+:
* Efficient forwarding with deep SID lists
* Operational Simplicity
* SRv6+ work may finish before SRv6
Efficient forwarding with deep SID Lists
----------------------------------------------------
SR customers have stated a firm requirement to support SR paths that contain 8
to 12 segments. They have also stated a requirement for implementations to
forward at line speed and without consuming excessive overhead bandwidth.
SRv6, as defined in draft-ietf-6man-segment-routing-header, cannot satisfy
these requirements. In order to support an SR path with 8 segments, SRv6 would
require a 128-byte SRH. Even if ASICs could process such a long SRH at line
speed, the bandwidth overhead would be prohibitive.
Therefore, one of the four solutions that you mention below is required to
make SRv6 deployable. While draft-ietf-6man-segment-routing-header is close to
maturity, the four competing solutions mentioned below are equally mature and
should be given equal consideration.
The four solutions are SRv6+, uSID, draft-li and draft-mirsky.
Operational Simplicity
-----------------------------
Network operators strive for operational simplicity. By loosely interpreting
(and sometimes bending) the requirements of RFCs 4291 and RFC 8200, SRv6
introduces architectural quirks that introduce operational complexity. The
following are architectural quirks of draft-ietf-6man-segment-routing-header:
* The Segment Routing Header (SRH) serves purposes other than routing.
Therefore, the SRH is sometimes required for packets that traverse the
least-cost path from source to destination
* The SRH and the IPv6 Authentication Header are incompatible.
* The IPv6 destination address determines whether an SRH is valid and how
it is processed. For example, if the IPv6 destination address contains one
locally instantiated value, the SRH might be processed in one particular way,
while if the IPv6 destination address contains another locally instantiated
value, the SRH might be totally invalid.
Draft-ietf-spring-srv6-network-programming promises more architectural quirks.
For example:
* Segment endpoints can insert and/or delete IPv6 extension headers
* An IPv6 packet can contain two Segment Routing headers
* IPv6 packets are no longer self-describing. For example, the Next Header
Field in the SRH can carry a value of No Next Header, even though the SRH is
followed by Ethernet payload.
Other emerging drafts promise still more architectural quirks. For example, in
draft-ali-6man-spring-srv6-oam, implementations need to examine the SRH even
when Segment Left equals zero. This is because the SRH has been overloaded to
carry OAM as well as routing information.
Furthermore, draft-filsfils-spring-net-pgm-extension-srv6-usid requires network
operators to obtain address space and number their networks in a particular way
to make routing work.
SRv6+ Work May Finish Before SRv6 work
--------------------------------------------------------
SRv6+ has been implemented on LINUX and is being implemented on JUNOS.
Implementation experience demonstrates that specification is fairly complete.
For example, there is no need for an SRv6+ OAM document. It's just IPv6 and
IPv6 OAM just works.
Furthermore, the SRv6+ specifications adhere to a strict interpretation of RFC
8200. Therefore, as they progress through the working group, they won't need to
overcome the objections that are inevitably encountered when stretching the
interpretation of a specification that is so fundamental as RFC 8200.
Thanks,
Ron
From: spring <spring-boun...@ietf.org<mailto:spring-boun...@ietf.org>> On
Behalf Of Rob Shakir
Sent: Sunday, August 4, 2019 5:04 PM
To: SPRING WG List <spring@ietf.org<mailto: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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