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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 18:49 UTC

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From: "Acee Lindem (acee)" <acee@cisco.com>
To: Jeff 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 18:49:18 +0000
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References: <20151118170601.5815.13593.idtracker@ietfa.amsl.com> <D2721A64.EAB62%aretana@cisco.com> <20151118182609.GD32083@pfrc.org>
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Cc: "isis-chairs@ietf.org" <isis-chairs@ietf.org>, "rtg-ads@ietf.org" <rtg-ads@ietf.org>, "Alvaro Retana (aretana)" <aretana@cisco.com>, "draft-ietf-bfd-seamless-base@ietf.org" <draft-ietf-bfd-seamless-base@ietf.org>, "ospf-chairs@ietf.org" <ospf-chairs@ietf.org>, "bfd-chairs@ietf.org" <bfd-chairs@ietf.org>, "l2tpext@ietf.org" <l2tpext@ietf.org>
Subject: Re: [L2tpext] Alvaro Retana's Discuss on draft-ietf-isis-sbfd-discriminator-02: (with DISCUSS)
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Hi Jeff, et al, 

> On Nov 18, 2015, at 1:26 PM, Jeffrey Haas <jhaas@pfrc.org> wrote:
> 
> On Wed, Nov 18, 2015 at 05:16:05PM +0000, Alvaro Retana (aretana) wrote:
>> Jeff/Reshad:
>> 
>> Hi!  How are you?
> 
> I *was* almost caught up with my BFD work post-IETF, thanks. :-)
> 
>> I need you to please drive the discussion below.  The outcome should be
>> consensus on how the mapping between multiple discriminators and
>> applications/use cases on a node should be handled.  I can guess at 3
>> potential outcomes:
>> 
>> 1. The "applications (e.g., OSPF/IS-IS)" should handle it.
>> 2. The S-BFD Base specification will detail how to do it (not requiring
>> additional work from the applications).
>> 3. We'll deal with this issue somewhere else (not requiring additional
>> work from the applications).
>> 
>> [Maybe there are more options.]
>> 
>> Please keep isis/ospf/l2tpext in the loop.
>> 
>> Even in the best case, we're probably going to need some clarification in
>> draft-ietf-bfd-seamless-base.
>> 
>> BTW, if you decide to follow this thread..  I fat fingered the address of
>> the l2tpext WG. :-(
> 
> 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? 

> 
> 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. 

Thanks,
Acee 


> 
> I leave comments about more clever things to do with this for the authors.
> 
> -- Jeff

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