Re: [spring] Chair Review of draft-ietf-spring-srv6-srh-compression-11

[Tom Herbert <[e-mail]>]

On Tue, Mar 26, 2024 at 4:03 PM Ron Bonica <[e-mail]> wrote:
>
> Sasha,
>
> At the moment when SRv6 diverges from  IPv6, the two evolutionary branches are identical. If SRv6 needs link locals, it can use them.
>
> However, SRv6 now has the freedom to evolve in ways that IPv6 cannot.

Hi Ron,

That assumes that SRv6 is forked from IPv6? It might be nice for
someone to write up an I-D to really clarify the relationship between
SRv6 and IPv6.

Tom

>
>                                                                   Ron
>
> Juniper Business Use Only
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> ________________________________
> From: Alexander Vainshtein <[e-mail]>
> Sent: Tuesday, March 26, 2024 4:24 PM
> To: Ron Bonica <[e-mail]>
> Cc: [e-mail] <[e-mail]>; Andrew Alston - IETF <[e-mail]>; Robert Raszuk <[e-mail]>; Tom Herbert <[e-mail]>; Alvaro Retana <[e-mail]>
> Subject: Re: [spring] Chair Review of draft-ietf-spring-srv6-srh-compression-11
>
>
> [External Email. Be cautious of content]
>
> Ron,
> I am not sure you can separate just the forwarding plane of SRv6 and IPv6.
>
> E.g., what would happen to all the IPv6 mechanisms that use link-local IPv6 addresses?
>
> Replicating these mechanisms does not make much sense to me.
>
> My 2c,
> Sasha
>
>
> Get Outlook for Android
>
>
> Juniper Business Use Only
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> ________________________________
> From: Ron Bonica <[e-mail]>
> Sent: Tuesday, March 26, 2024 8:36:49 PM
> To: Alexander Vainshtein <[e-mail]>
> Cc: [e-mail] <[e-mail]>; Andrew Alston - IETF <[e-mail]>; Robert Raszuk <[e-mail]>; Tom Herbert <[e-mail]>; Alvaro Retana <[e-mail]>
> Subject: [EXTERNAL] Re: [spring] Chair Review of draft-ietf-spring-srv6-srh-compression-11
>
> Sasha,
>
> Good point. In my previous email, I didn't mean suggest that we should divorce SRv6 from the entire suite of Internet protocols. I only meant that we should divorce the SRv6 forwarding plane from the IPv6 forwarding plane. BGP could continue to distribute SIDS exactly as is distributes MPLS service labels today.
>
> You bring up another good point about the parallel evolution of SRv6 and IPv6. Yes, this is an engineering trade off. If you divorce SRv6 from IPv6, and IPv6 develops a useful new feature, SRv6 might need to develop that feature, too. However, if you bind SRv6 to IPv6, SRv6 must strictly adhere to IPv6 standards, both now and in the future.
>
> Which is more painful?
>
>                                                                        Ron
>
> Juniper Business Use Only
>
> ________________________________
> From: Alexander Vainshtein <[e-mail]>
> Sent: Tuesday, March 26, 2024 1:56 PM
> To: Ron Bonica <[e-mail]>
> Cc: [e-mail] <[e-mail]>; Andrew Alston - IETF <[e-mail]>; Robert Raszuk <[e-mail]>; Tom Herbert <[e-mail]>; Alvaro Retana <[e-mail]>
> Subject: RE: [spring] Chair Review of draft-ietf-spring-srv6-srh-compression-11
>
>
> [External Email. Be cautious of content]
>
> Ron and all,
>
> I respectfully disagree with the proposal of separation of SRv6 from the existing IPv6.
>
>
>
> IMHO and FWIW the most important added value of SRv6 is its ability to provide BGP-based overlay services without any changes in the P routers as described in Introduction of RFC 9252:
>
>
>
> To provide SRv6 service with best-effort connectivity, the egress PE signals an SRv6 Service SID with the BGP overlay service route. The ingress PE encapsulates the payload in an outer IPv6 header where the destination address is the SRv6 Service SID provided by the egress PE. The underlay between the PEs only needs to support plain IPv6 forwarding [RFC8200].
>
>
>
> To me this means that SRv6 services can benefit from incremental deployment when new forwarding capabilities (implementation of SRv6 Endpoint Behaviors) would be initially available just in the relevant PEs.
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>
>
> And best-effort BGP-based SRv6 services would scale up much better than best-effort BGP-based services on top of a SR-MPLS underlay because:
>
> With SR-MPLS, the forwarding HW of the ingress PE would have to maintain at least one dedicated egress encapsulation information element for the local representation of each service instance in each egress PE of this service (the label stack that delivers the packet to the relevant egress PE and the label that identifies the relevant service in this egress PE)
> With SRv6, the forwarding HW of the ingress PE would have to maintain only a dedicated egress encapsulation information element for each local adjacency of this PE.
>
> IMHO and FWIW the flex-algo approach extends the above scalability considerations to BGP-based SRv6 services that require some kind of traffic engineering.
>
>
>
> All these advantages would be lost if SRv6 were separated from IPv6. Such separation would require, at the very least:
>
> HW (or FW) upgrades that would identify received SRv6 packets based on their new Ethertype – across the entire SRv6 network
> SW upgrades supporting new/modified routing protocols dedicated for SRv6 – also across the entire SRv6 network.
>
>
>
> From my POV, SRv6 should try to minimize its deviations from the “normal” IPv6 (e.g., the differences in the address architecture), clearly define them and avoid all attempts to violate the IPv6 rules that do not belong to the “deviated” area.
>
>
>
> My 2c,
>
> Sasha
>
>
>
>
> Juniper Business Use Only
>
> From: spring <[e-mail]> On Behalf Of Ron Bonica
> Sent: Tuesday, March 26, 2024 7:14 PM
> To: Tom Herbert <[e-mail]>; Alvaro Retana <[e-mail]>
> Cc: [e-mail]; Andrew Alston - IETF <[e-mail]>; Robert Raszuk <[e-mail]>
> Subject: [EXTERNAL] Re: [spring] Chair Review of draft-ietf-spring-srv6-srh-compression-11
>
>
>
> Working Group,
>
>
>
> Might  SRv6 progress much more quickly if we did the following:
>
>
>
> ·       Divorce SRv6 from IPv6
>
> ·       Give SRv6 its own ethertype
>
> ·       Let SRv6 progress along its own evolutionary trajectory, unencumbered by IPv6 restrictions
>
>
>
> At very least, this divorce would end the long and painful debates regarding IPv6 compliance. And would it give SRv6 more degrees of freedom as it evolves,
>
>
>
> As far as I can see, the only benefit of binding SRv6 to IPv6 is in the expectation that IPv6-enabled hardware won't have to change too much to support SRv6. This benefit might still be realized if SRv6 doesn't deviate too much from IPv6.
>
>
>
> My question is not rhetorical. Maybe I am missing something, but is there any real benefit in continuing to bind SRRv6 to IPv6?
>
>
>
>                                                            Ron
>
>
>
> Juniper Business Use Only
>
> ________________________________
>
> From: Tom Herbert <[e-mail]>
> Sent: Monday, March 25, 2024 3:40 PM
> To: Alvaro Retana <[e-mail]>
> Cc: Robert Raszuk <[e-mail]>; Andrew Alston - IETF <[e-mail]>; Ron Bonica <[e-mail]>; [e-mail] <[e-mail]>; Joel Halpern <[e-mail]>
> Subject: Re: [spring] Chair Review of draft-ietf-spring-srv6-srh-compression-11
>
>
>
> [External Email. Be cautious of content]
>
>
> On Mon, Mar 25, 2024 at 12:31 PM Alvaro Retana <[e-mail]> wrote:
> >
> > Tom:
> >
> > Hi!
> >
> > I understand your point.
> >
> > I put the option out there because it came up at last week’s spring meeting and it should be discussed.
>
> Alvaro,
>
> This seems to come back to the fundamental question: is SRv6 still
> IPv6 or is it a new protocol. If it's IPv6 then it should adhere to
> all the requirements and expectations of IPv6, if it's a new protocol
> that is going to diverge from the standard IPv6 then maybe it needs
> its own EtherType and standards development path.
>
> Tom
>
>
> >
> > Thanks!
> >
> > Alvaro.
> >
> >
> > On March 25, 2024 at 2:58:48 PM, Tom Herbert ([e-mail]) wrote:
> >
> > On Mon, Mar 25, 2024 at 11:17 AM Alvaro Retana <[e-mail]> wrote:
> > >
> > > FWIW, I agree with most of what Joel wrote. ;-)
> > >
> > > I see another path forward: Given that the issue is constrained to an SR domain, the draft could also point out the issues as operational/deployment considerations. Operators can then make an informed decision on whether they want to/can use C-SIDs without an SRH in their network. This path forward (or leaving it out of scope, as Joel suggests below) is something the spring WG can reach consensus on by itself (i.e., without needing to consult or agree with other WGs).
> >
> > Alvaro,.
> >
> > This wouldn't be robust and would seem to violate the "be conservative
> > in what you send clause". Punting this to the operators doesn't seem
> > practical either, in an even moderately large network they wouldn't be
> > able to know all the potential problems they might hit in devices.
> > They're about one misconfiguration away from having to debug a rather
> > unpleasant problem. For instance, if operator gets a packet trace from
> > a router they would see a whole bunch of packets with bad checksums,
> > but they would have no way of knowing if these were cases of segment
> > routing or actually corrupted packets.
> >
> > Tom
>
>
>
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