Re: [PWE3] BFD for MPLS PWs

On Aug 30, 2006, at 2:37 PM, Luca Martini wrote:

> Thomas D. Nadeau wrote:
>>
>>> 4. The draft indicates that PWs should be torn down when the CV  
>>> or CC
>>> types change. IMO, we should only tear down when strictly  
>>> necessary. If
>>> a node has the LSP Ping feature disabled, but is then turned on,  
>>> there
>>> is no reason why the PWs need to be torn down.
>>
>>     We originally added this to simplify implementation, but
>> I now see why it is important to allow a change of this on the fly
>> without disrupting the data flow for the PW. Let me suggest that we
>> allow changes only after a subsequent transmission of the interface
>> parameters TLV with new capabilities advertisements. In this case,
>> the sending PE MAY choose to send a different payload type. But
>> as originally stated, once it starts sending it, it MUST continue
>> with that type.  We want to avoid having to entertain different
>> payload types on the fly, which I think does complicate the
>> implementations. Although we might want to relax the MUST to a
>> SHOULD.
>>
>>     --Tom
>>
> Actually quoting RFC4447:
> "
>  -  Interface Parameter Sub-TLV
>
>      This variable-length TLV is used to provide interface-specific
>      parameters, such as attachment circuit MTU.
>
>      Note that as the "interface parameter sub-TLV" is part of the  
> FEC,
>      the rules of LDP make it impossible to change the interface
>      parameters once the pseudowire has been set up.  Thus, the
>      interface parameters field must not be used to pass information,
>      such as status information, that may change during the life of  
> the
>      pseudowire.  Optional parameter TLVs should be used for that
>      purpose.
> "
>
> So the interface parameter sub-TLV cannot be "updated" without  
> issuing  a label withdraw message and re-advertising the FEC.

	Good point. We should leave the text as we originally
had it, which agreed with your reference.

	--Tom

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