Re: [OSPF] [Isis-wg] Mail regarding draft-ietf-ospf-segment-routing-extensions

Rob Shakir <rjs@rob.sh> Mon, 29 December 2014 09:41 UTC

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From: Rob Shakir <rjs@rob.sh>
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To: Shraddha Hegde <shraddha@juniper.net>
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Subject: Re: [OSPF] [Isis-wg] Mail regarding draft-ietf-ospf-segment-routing-extensions
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> On 29 Dec 2014, at 09:33, Shraddha Hegde <shraddha@juniper.net> wrote:
> 
> <Shraddha> It is likely that some application wants to use the node-sids when the strict path for performance sensitive traffic matches with that of the SPF  for some segments or for the entire path. 
> 

There is nothing stopping it doing so, but it cannot deterministically say that the path will remain coherent with the one that it expects for multiple reasons:

1) Nodes along the path may select a subset of ECMPs, the performance of which may vary.
2) There may be topology changes (triggered by failure or not) which mean that the shortest-path may change.

Given that either of these can result in performance variance, it’s very likely (from a practical standpoint) that the traffic must be able to live with FRRs too - hence it being unclear to me that there’s a requirement for an ‘unprotected’ Node SID.

r.