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

Shraddha Hegde <shraddha@juniper.net> Tue, 21 November 2017 04:42 UTC

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From: Shraddha Hegde <shraddha@juniper.net>
To: Peter Psenak <ppsenak@cisco.com>, "Acee Lindem (acee)" <acee@cisco.com>, "draft-hegdeppsenak-isis-sr-flex-algo@ietf.org" <draft-hegdeppsenak-isis-sr-flex-algo@ietf.org>
CC: "isis-wg@ietf.org" <isis-wg@ietf.org>
Thread-Topic: ISIS SR Flexible Algorithm (Resending with alias correction)
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Date: Tue, 21 Nov 2017 04:12:12 +0000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/isis-wg/1MfqJX1yRUacBqxSjMfNtgYsIGM>
Subject: Re: [Isis-wg] ISIS SR Flexible Algorithm (Resending with alias correction)
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Peter/Acee,

Lets assume 1.1.1.1 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.

Rgds
Shraddha



-----Original Message-----
From: Peter Psenak [mailto:ppsenak@cisco.com] 
Sent: Tuesday, November 21, 2017 3:35 AM
To: Acee Lindem (acee) <acee@cisco.com>; draft-hegdeppsenak-isis-sr-flex-algo@ietf.org
Cc: isis-wg@ietf.org
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 algorithm).

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 not.

thanks,
Peter

>
> Thanks,
> Acee

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