Re: [mpls] Martin Vigoureux's Yes on draft-ietf-mpls-sfc-05: (with COMMENT)

"Adrian Farrel" <adrian@olddog.co.uk> Thu, 07 March 2019 15:18 UTC

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From: "Adrian Farrel" <adrian@olddog.co.uk>
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Subject: Re: [mpls] Martin Vigoureux's Yes on draft-ietf-mpls-sfc-05: (with COMMENT)
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Hi Martin,

Thanks for your thoughts.

> COMMENT:
>
> I know I'm being too pernickety:

As is your right 😉

> You say:
>   o  An SFF MUST decrement the TTL by one each time it performs a
>      forwarding lookup.
> but in the examples you also say:
>   b.  When the packet arrives at SFFa it strips any labels associated
>       with the tunnel that runs from the classifier to SFFa.  SFFa
>       examines the top labels and matches the SPI/SI to identify that
>       the packet should be forwarded to SFa.  The packet is forwarded
>       to SFa unmodified.
> and
>   d.  SFFa modifies the SI in the lower label stack entry (to 254) and
>       uses the SPI/SI to look up the forwarding instructions.
>
> It could look as two forwarding lookup, which, according to the
> requirement, could lead to two TTL decrements.  I do read in step b that the packet is
> forwarded unmodified, and read in Section 6 "The TTL in SF label stack entry is
> decremented once for each forwarding hop in the SFP" but still I wonder if some
> clarification wouldn't be beneficial.

Oh, dear. Yes, you're right about the word "forward". It crops up too often with too many meanings.

I think the tidies solution is to change the first quote to say...

   An SFF MUST decrement the TTL by one each time it performs a
   lookup to forward a packet to the next SFF.

> nits:
>   TTL:  The TTL fields in the SFC Context label stack entry SF label
>      stack entry SHOULD be set to 1 as stated in Section 5,
> Do you mean: SFC Context label stack entry *and* SF label stack entry ?

Yup

> s/document)./document./

Ack

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