Re: [Idr] Review Updates to draft-ietf-idr-bgp-prefix-sid

[Robert Raszuk <[e-mail]>]

Hi Sue,

Well Acee said himself few email back:

"Dear Alvaro and IDR WG:



     There is one more change we’d like to make to the draft that requires
WG approval."


I maybe just don't 'know what formally this "WG approval" is :)


Thx,
R.





On Sun, Feb 18, 2018 at 4:54 PM, Susan Hares <[e-mail]> wrote:

> Robert and Acee:
>
>
>
> If we do “open surgery”, this document will need to go back through the
> process (WG LC, IETF LC, and IESG Review).
>
>
>
> Sue Hares
>
> IDR co-chiar
>
>
>
> *From:* Idr [mailto:[e-mail]] *On Behalf Of *Robert Raszuk
> *Sent:* Sunday, February 18, 2018 5:57 AM
> *To:* Acee Lindem (acee)
> *Cc:* [e-mail]
> *Subject:* Re: [Idr] Review Updates to draft-ietf-idr-bgp-prefix-sid
>
>
>
> Hi Acee,
>
>
>
> Since we are at the open surgery of this draft there is one more point
> which did not got resolved during our offline discussion. Feedback from WG
> is welcome here.
>
>
>
> The draft RECOMMENDS the following procedure in case of a conflict:
>
>
>
> ... it is RECOMMENDED that the first prefix using the label index is selected.
>
>
>
> In BGP there is no guarantee about ordered delivery of BGP prefixes.  It
> may work such in some specific topologies but not in any arbitrary one. So
> if we recommend to pick one prefix on R1 and different prefix on R2 and
> install in forwarding the same SID for those I am afraid the data plane
> will get quite severely messed up and even finding it during
> troubleshooting will be quite hard.
>
>
>
> Also as pointed out already MPLS anycast SID may on purpose use the same
> label across nodes according to draft-ietf-spring-mpls-anycast-segments-02.
> Now if we want to accomplish the same in BGP we would need to advertise
> different prefixes with the same SID (in MPLS-SR index). the above
> paragraph does prevents that. Note that adding and advertising the _same_
> prefix from different nodes will not work as BGP speakers may pick only one
> (best path) and use it for forwarding. IBGP or EBGP multipath may not
> always be enabled/use same set.
>
>
>
> The crux of the issue when advertising SIDs in BGP is not so much about
> prefixes, but their next hops which unfortunately the draft does not even
> mention once.
>
>
>
> Kind regards,
>
> Robert.
>
>
>