Re: [mpls] A question about draft-ietf-mpls-sfl-framework

Stewart Bryant <> Thu, 03 January 2019 14:27 UTC

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To: Alexander Vainshtein <>, "" <>
Cc: "" <>, Shell Nakash <>, Jun Ye <>
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From: Stewart Bryant <>
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Date: Thu, 3 Jan 2019 14:27:10 +0000
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Subject: Re: [mpls] A question about draft-ietf-mpls-sfl-framework
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On 25/12/2018 11:45, Alexander Vainshtein wrote:
> Dear authors of draft-ietf-mpls-sfl-framework 
> <>;,
> I have a question about use of Synonymous Flow Labels in the when 
> application labels are present.
> The relevant text in Section 4.1 of the draft says:
>    At the egress LSR the LSP label is popped (if present).  Then the SFL
>    is processed in exactly the same way as the corresponding application
>    label would have been processed.
> If the application label has been statically configured in the egress 
> LSR,  then, presumably, so would be each of the Synonymous labels.
> However, if the application label has been dynamically allocated by 
> the egress LSR and advertised to ingress LSR using some control plane 
> mechanisms, then the synonymous labels would also have to be 
> dynamically allocated and advertised by the same control plane mechanisms.
Not necessarily.

We had a proposal for a simple control plane that I propose to refresh:

The idea with this is that the application control protocol runs as 
normal and this protocol modifies the label for SFL purposes.

There was a lot of interest in the WG at the time for modifying each and 
every control protocol, but there is not much interest in writing the 
drafts needed to do it.

> The draft in question is a framework draft and does not discuss any 
> control plane issues (at least I have not found any mention of such 
> issues in the text).
> I wonder if any work on control plane mechanisms for advertisement of 
> synonymous labels is going on or planned. ( A quick search in the 
> documents of the MPLS, BESS and PALS WGs did not find any relevant 
> documents).
Only the one I cite above.

I would be more than willing to work with anyone (actively or just as a 
reviewer) that wanted to write the control plane drafts.

> If the intended applicability of the SFL framework is just for 
> statically configured application labels, this should be explicitly 
> stated in the draft IMHO.
No, I think the intent was always that there would be a control plane if 

Best regards


> Your timely feedback would be highly appreciated.
> Regards, and lots of thanks in advance,
> Sasha
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