Re: [L2tpext] Alvaro Retana's Discuss on draft-ietf-isis-sbfd-discriminator-02: (with DISCUSS)

"Acee Lindem (acee)" <acee@cisco.com> Wed, 18 November 2015 19:29 UTC

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From: "Acee Lindem (acee)" <acee@cisco.com>
To: Jeffrey Haas <jhaas@pfrc.org>
Thread-Topic: Alvaro Retana's Discuss on draft-ietf-isis-sbfd-discriminator-02: (with DISCUSS)
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Date: Wed, 18 Nov 2015 19:29:27 +0000
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References: <20151118170601.5815.13593.idtracker@ietfa.amsl.com> <D2721A64.EAB62%aretana@cisco.com> <20151118182609.GD32083@pfrc.org> <9F972E95-3DBC-45C7-8D25-5A3490942480@cisco.com> <20151118185941.GA30062@pfrc.org>
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Subject: Re: [L2tpext] Alvaro Retana's Discuss on draft-ietf-isis-sbfd-discriminator-02: (with DISCUSS)
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Jeff, 

On 11/18/15, 1:59 PM, "Jeffrey Haas" <jhaas@pfrc.org> wrote:

>Acee,
>
>On Wed, Nov 18, 2015 at 06:49:18PM +0000, Acee Lindem (acee) wrote:
>> > We'll give the authors a chance to reply, but basically:
>> > - discriminators must already be domain-wide unique.
>> > - The uniqueness property tends to imply provisioning.
>> > - Thus the foreknowledge for the mapping is probably implied.
>> 
>> I hate to be a killjoy, but if everything is pre-provisioned, what is
>>the benefit of advertising the S-BFD discriminators in the IGPs?
>
>I did say "imply". :-)
>
>There's also a slight difference between provisioning for purposes of
>making
>sure things are unique domain wide and putting a copy of that mapping on
>every single node.  That's at least one reason to distribute in the IGP.
>
>And the other case would be something like derived from router-id.

In any case, it seems that multiple reviewers have asked from some
discussion of how this mapping is or at least might be done and I don’t
think it belongs in the IGP drafts.

Thanks,
Acee 


>
>> > See section 5, second to last paragraph for reinforcement that it's a
>>local
>> > matter.
>> > 
>> > The better questions are "why would you give a given node more than
>>one
>> > discriminator?"  The typical case is likely to be for scaling the
>>number of 
>> > BFD sessions on that node.
>> 
>> For this use case, pre-provisioning could be avoided with a standard
>>algorithm to choose among multiple discriminators.
>
>Even for this case, I'd hesitate to be too proscriptive.  Trying to
>describe
>an algorithm to provide load-balancing domain-wide with unknown loads is
>likely to be wrong... and hard to compete with "pick one at random" in
>many
>cases.





>
>-- Jeff