Re: [spring] Understanding the replication draft

Robert Raszuk <robert@raszuk.net> Wed, 01 July 2020 19:27 UTC

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From: Robert Raszuk <robert@raszuk.net>
Date: Wed, 1 Jul 2020 21:27:33 +0200
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To: Rishabh Parekh <rishabhp@gmail.com>
Cc: Joel Halpern Direct <jmh.direct@joelhalpern.com>, "spring@ietf.org" <spring@ietf.org>
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Subject: Re: [spring] Understanding the replication draft
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Hi Rishabh,

 > Of course, care must be
> taken to avoid the "explosion" as you describe it. G-SID-2 has to map
> to a unique node; for example, it may be an Anycast-SID that takes
> packet to distinct nodes from each of the downstream node, or the
> downstream nodes can be border nodes connecting to other segment
> routing domains where G-SID-2 resolves to distinct nodes in each
> domain.

I think you are stretching it too thin.

See even if G-SID-2 is anycast SID you have zero assurance that physical
nodes packets will land on would be at all diverse.

Likewise crossing domains yet providing identical global SID now to be a
different node in each such domain to me is not a realistic example.

I think we have two options:

A) Firmly state that replication SID MUST be the last one on the stack

B) Instead of real SID after the replication SID provide a binding SID
which locally will be mapped to a different SID list imposed to
each replicated flow.

What is currently in the draft seems to be very counterintuitive and IMHO
will result in operational difficulties.

Thx a lot,
R.