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RE: [OSPF] Genart last call review of draft-ietf-ospf-segment-routing-extensions-19

"Les Ginsberg (ginsberg)" <ginsberg@cisco.com> Thu, 12 October 2017 19:30 UTC

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From: "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
To: "Peter Psenak (ppsenak)" <ppsenak@cisco.com>, Dan Romascanu <dromasca@gmail.com>, "gen-art@ietf.org" <gen-art@ietf.org>
CC: "draft-ietf-ospf-segment-routing-extensions.all@ietf.org" <draft-ietf-ospf-segment-routing-extensions.all@ietf.org>, "ietf@ietf.org" <ietf@ietf.org>, "ospf@ietf.org" <ospf@ietf.org>
Subject: RE: [OSPF] Genart last call review of draft-ietf-ospf-segment-routing-extensions-19
Thread-Topic: [OSPF] Genart last call review of draft-ietf-ospf-segment-routing-extensions-19
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Date: Thu, 12 Oct 2017 19:30:18 +0000
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In regards to

> > 4. Section 3.3:
> >
> > 'The originating router MUST NOT advertise overlapping ranges.'
> >
> > How are conflicts resolved at receiver?
> 
> SRLB sub-TLV is not used by routers running ISIS. The advertisement is only
> there for the benefit of external entities such as controllers so they can
> determine what labels are available for assignment. We do not define
> controllers behavior in our drafts.
> 
> >
[Les:] SRLB usage is not the same as SRGB usage.

SRLB is a local space for each node to allocate node private labels. There is no notion of conflicting usage e.g. Node A can use 1000 as an adj-sid for one of its links and Node B can use SID 1000 as an adj-sid for one of its links and this is not a conflict. In other words the scope of the SIDs is local to the advertising node.

Further, nodes are NOT required to validate that a private SID (such as an adj-sid) is allocated from the SRLB of the advertising node - it is legal to assign a SID from outside of this space - so - as Peter has indicated - other routers do not make use of SRLB advertisements. IT is there for the convenience of external entities only.

It should be obvious that advertising overlapping ranges makes the advertisement ambiguous. Not sure what else needs to be said.

???

    Les

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