Ron & SPRING WG chairs,

Through this discussion we first have seen a debate if we need one or more
data planes to compress SIDs in SRv6. WG clearly stated we need one.

Following that we have observed a first terminology shift to see if asking
how many solutions should be supported will work any better. To that many
WG members clearly stated that they support one solution.

Well please notice that the draft in question in its introduction states:

Abstract

   This document defines a compressed SRv6 Segment List Encoding in the
   Segment Routing Header (SRH).  *This solution* does not require any SRH
   data plane change nor any SRv6 control plane change.  *This solution*
   leverages the SRv6 Network Programming model.

So based on my understanding of English the entire draft talks about a
single solution.

Then suddenly a new question popped up: how many behaviours are acceptable.

I bet number of folks including myself said "one" keeping in mind previous
discussions and the definition of "one" meaning based on the SRv6 data
plane in compliance to [RFC8402], [RFC8754] and [RFC8986].

Interestingly enough the draft in question defines not behaviours but
flavors as new variants of the already defined behaviors in Standards Track
RFCs. Namely it defines:

4.1.  NEXT-C-SID Flavor
4.2.  REPLACE-C-SID Flavor

The newly defined behaviour End.XPS is optional.

So if there is anything to ask here is to check if WG is ok with two
flavors or not. I do not recall that question has ever been asked formally
during the WG adoption call.

With that let's note that optimal compressed SID size may be different
network to network. One size does not fit all. Draft says:

6.1.  C-SID Length

   The NEXT-C-SID flavor supports both 16- and 32-bit C-SID lengths.  A
*   C-SID length of 16-bit is recommended.*

   The REPLACE-C-SID flavor supports both 16- and 32-bit C-SID lengths.
*   A C-SID length of 32-bit is recommended.*

While I personally think 8-bit should be an option, if we choose a single
flavor we will introduce suboptimality for no good reason. Hardware
capable of supporting any flavor clearly can do LPM on locator. Also
hardware capable of supporting one flavor can support few other flavors as
this is pretty much just an offset game.

Kind regards,
Robert



On Tue, Oct 5, 2021 at 9:43 PM Ron Bonica <rbonica=
40juniper....@dmarc.ietf.org> wrote:

> Pablo,
>
>
>
> Ae you sure? Please look at the question as Joel asked it (
> https://mailarchive.ietf.org/arch/msg/spring/nS2gnQ_jxvpbmcxs_d3JAbUCT1I/
> ).
>
>
>
>
> Ron
>
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