Re: [Isis-wg] How to handle multiple overlapping SRGB ranges

<bruno.decraene@orange.com> Thu, 25 June 2015 13:58 UTC

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From: <bruno.decraene@orange.com>
To: "Stefano Previdi (sprevidi)" <sprevidi@cisco.com>, "isis-wg@ietf.org list" <isis-wg@ietf.org>
Thread-Topic: How to handle multiple overlapping SRGB ranges
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Date: Thu, 25 Jun 2015 13:58:26 +0000
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Subject: Re: [Isis-wg] How to handle multiple overlapping SRGB ranges
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> From: Isis-wg [mailto:isis-wg-bounces@ietf.org] On Behalf Of Stefano Previdi (sprevidi)
> 
> All,
> 
> there's an open question that requires the wg to agree
> 
> The issue here is related to SRGB ranges advertised within the SR-Cap SubTLV.
> 
> The question is: what a receiving router should do when receiving SRGB
> ranges that overlaps ?

Presumably, the question is equally applicable to OSPF, so I'm adding the ospf WG in the discussion.

 
> Knowing that the spec mandates a single SR-Cap SubTLV, the overlap may
> happen only within the same SR-Cap subTLV and therefore it is clearly a local
> misconfiguration or an implementation bug in the router originating the SR-
> Cap.
> 
> Personally, I would recommend to ignore the whole SRGB (not only the
> overlapping ranges) from the faulty router. Ignoring only the overlapping
> ranges would not work since the whole index space is affected anyway.

Personally, I would recommend ignoring the overlapping SRGB Descriptor and the subsequent ones. But I'd rather keep the SRGB descriptors which are before (the overlaps) as they do not pose a problem. Keeping them preserve the forwarding of the global Segments using them. This seems inline with the IETF  Robustness Principle https://tools.ietf.org/html/rfc1122#section-1.2.2

"      1.2.2  Robustness Principle

         At every layer of the protocols, there is a general rule whose
         application can lead to enormous benefits in robustness and
         interoperability [IP:1]:

                "Be liberal in what you accept, and
                 conservative in what you send"

         Software should be written to deal with every conceivable
         error, no matter how unlikely; sooner or later a packet will
         come in with that particular combination of errors and
         attributes, and unless the software is prepared, chaos can
         ensue."
[...]
"host software should be prepared, not
         just to survive other misbehaving hosts, but also to cooperate
         to limit the amount of disruption such hosts can cause to the
         shared communication facility."

In particular "cooperate to limit the amount of disruption"

Thanks
/Bruno
 
> There are different opinions on how the receiving router should behave.
> Ideally, we should converge towards a single solution so feel free to comment.
> 
> Thanks.
> s.
> 
> _______________________________________________
> Isis-wg mailing list
> Isis-wg@ietf.org
> https://www.ietf.org/mailman/listinfo/isis-wg

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