The MPLS WG Archive

["Adrian Farrel" <adrian@olddog.co.uk>]

Hi Huub,

>> The implication of the text is that you can have a packet of the
>> form:
>>
>> LSE (RFC3032)
>> Sequence number
>> LSE (RFC3032)
>> Payload
>>
>> Is that correct?
>
> This is also what I read, and apparently Neil does as well.
>
>> If so what is the setting of the S bit (See RFC3032) in each
>> case?
>
> Because the text does not mention any altering of the S-bit
> I assume they do not change.

Ah, so either setting of the S-bit is allowed?

> I agree with Neil (see his 2002 post) that this requires a
> very carefull configuartion of the network. Checking that
> both ends support this feature and closely guard the connectivity
> for both diverse routes.

With the S-bit, careful config is needed.

Without the S-bit it seems like a router that popped a label would expect 
the next thing on the stack to also be a label, but would actually find a 
magic sequence number. Although you could config around this (since the pop 
action must be installed) this is a new MPLS behavior. At the least it is a 
new LFIB action that is not previously described in any MPLS documentation.

> Note that this text is in an appendix, so it does not form
> an integral part of the recommendation, i.e. it is not mandatory.

Hmmm.

Shouldn't there be a specification of:
- what must be supported
- what can also be attempted

I think Stewart's question is quite helpful here. Do we have any idea of 
what deployed implementations do?

Cheers,
Adrian



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