Re: [Idr] Progressing draft-bhatia-bgp-multiple-next-hops-01.txt

["Glen Kent" <glen.kent at gmail.com>]

Curtis,

> > Path 1 - NLRI 192/8 AS_PATH {10 20} LOCAL_PREF 100 NEXT_HOP 1.1.1.1
> >
> > Path 2 - NLRI 192/8 AS_PATH {10 20} LOCAL_PREF 189 NEXT_HOP 1.1.1.1
>
> If this came from the same router then complain because the sender of
> this is broken.

This is exactly what a receiver will receive if add-paths is
implemented, because you dont differentiate between paths. You blindly
flood all the paths that you receive.

> On the priciple of "being liberal in what you accept" just toss the
> second path.

If the receiver has to ignore all such paths then why is add-paths
sending them in the first place?


> > How does this router determine which route is being used by the
> > upstream? I dont think we should progress any proposal without
> > incorporating ways to indicate which path is being actually used in
> > the forwarding.
>
> If its a multipath it is considering both to be valid.  This may be
> possible at an IX if next-hop-self is not set and there is an odd set
> of routing policies.  btw- no where in BGP does it require that
> routing policies be sane (and they can be seemingly quite wierd).  If
> the AS are 65010, 65020, and 65030, this is perfectly valid in an AS
> confederation setup.  In AS confederations you'd just forward to
> 1.1.1.1 but retain the AS paths for readvertising.

No, you didnt get my question at all. My point is that we need to
explicitly mark the route being used in fwding, as otherwise the peer
receiving multiple paths can never know which path is being used by
the router advertising these routes. You need this information for
obvious reasons. See Jeffs mail for more details.

None of the proposals currently do this which to me is rather blasphemous.

Glen

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