Re: [OSPF] Poll for WG adoption of draft-hegde-ospf-node-admin-tag

Hannes Gredler <hannes@juniper.net> Wed, 03 September 2014 11:01 UTC

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Date: Wed, 3 Sep 2014 13:01:27 +0200
From: Hannes Gredler <hannes@juniper.net>
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To: Peter Psenak <ppsenak@cisco.com>, <bruno.decraene@orange.com>, Rob Shakir <rjs@rob.sh>
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Subject: Re: [OSPF] Poll for WG adoption of draft-hegde-ospf-node-admin-tag
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hi peter,

the question is not so much which registry is better;

we have existing proof-point (rlfa-spec not containing any capabilities)
that there may be the possibility that:

- a well-known, protocol specific tag does not exist
- the operator problem (excluding/including certain nodes
   from PQ capability) still does exist

so it looks like we have a practical case in favor of bruno's argument.


let me draw also some analogy to tagging of IP prefixes here:
draft-hegde-ospf-node-admin-tag is a generic vehicle just as
http://datatracker.ietf.org/doc/rfc5130/ has been conceived for
IP prefixes. - it is correct for the problem described in
RFC5130 we could have been applying application-specific
bits in IP prefixes that control the leaking behavior.

however a different model has been chosen:

1) use generic, application-context-free tags for a prefix
2) write the leaking policy which refers to those tags.

i find the flexibility of that model appealing and i'd
like to have something similar for "nodes" on link-state
graphs.

/hannes

On 9/3/14 12:32, Peter Psenak wrote:
>>
>> I agree as a general rule. Yet IMHO we should not kill this
>> possibility. In particular for feature allowing incremental deployment
>> & interaction with non-compliant nodes.
>> One example would have been Remote LFA (RLFA):
>> - the PLR (FRR node) needs to be RLFA compliant. Therefore (potential)
>> communication between PLR regarding their capabilities can be done
>> using IANA/implemented code point.
>> - the PQ node (Merge Point) does not need to be RLFA compliant. And we
>> should keep this property to ease incremental deployment. Therefore
>> communication between PQ and PLR regarding PQ capabilities should/may
>> be done using node tag.  RLFA spec could have defined an IANA
>> registered node tag to be used by PQ (configured by the network
>> operator) to exclude them as PQ candidate. e.g. for PQ node not
>> accepting T-LDP session or nodes which should not be used as PQ per
>> policy.
>
> why is "IANA registered node tag" any better then IANA registered
> capability bit in the above case?