Re: [Isis-wg] ISIS SR Flexible Algorithm (Resending with alias correction)

"Acee Lindem (acee)" <> Tue, 21 November 2017 11:39 UTC

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From: "Acee Lindem (acee)" <>
To: Shraddha Hegde <>, "Peter Psenak (ppsenak)" <>, "" <>
CC: "" <>
Thread-Topic: ISIS SR Flexible Algorithm (Resending with alias correction)
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Date: Tue, 21 Nov 2017 11:39:10 +0000
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Subject: Re: [Isis-wg] ISIS SR Flexible Algorithm (Resending with alias correction)
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Hi Shraddha, 

The situation I’m talking about is not when the same SID is advertised. It
is simpler since the two IS-IS routers advertise different SIDs but use
different algorithms. In this case, SR-domain ingress router local policy
would dictate which topology and/or algorithm is selected.


On 11/20/17, 11:12 PM, "Shraddha Hegde" <> wrote:

>Lets assume is advertised by two nodes A and B.
>A assigns a SID 10 :algo 200
>B assigns SID 10: algo 201
>According to conflict resolution draft section 3.4 SID conflicts
>Will be examined for algorithms and smallest algo wins
>So remote nodes will program nexthops for SID 10 based on algo 200.
>I think this case is addressed in conflict resolution draft.
>It would be better to handle all the conflict situation in conflict
>resolution draft
>Rather than putting different pieces in different drafts.
>-----Original Message-----
>From: Peter Psenak []
>Sent: Tuesday, November 21, 2017 3:35 AM
>To: Acee Lindem (acee) <>om>;
>Subject: Re: ISIS SR Flexible Algorithm (Resending with alias correction)
>Hi Acee,
>On 20/11/17 19:19 , Acee Lindem (acee) wrote:
>> Hi Shraddha, Peter, et al,
>> The comment on the draft I had was that the conflict case where two
>> ISIS routers advertise the same multi-homed prefix with a different
>> algorithm needs to be covered. I wouldn’t try and optimize for this
>> and would just do whatever is simplest but avoids loops (e.g., log the
>> situation and prefer the path computed with the lowest numbered
>prefix can have SIDs for many algorithms. Prefix-SID for one algorithm is
>independent and orthogonal to prefix-SID for any other algorithm.
>There is no need for all sources of the multi-homed prefix to include the
>same set of Algo-SIDs. Each source can advertise an independent set.
>The case is similar to Alg-0 SID, where prefix is advertised from two
>different sources and one source advertise the Alg-0 SID and other does
>> Thanks,
>> Acee