Simpler, with B and C peered: F / \ B---C \ / A
If B does not send the /24 to F, then F will send all the traffic to C, even if A wanted a load balance. Maybe I could ask the community: Why do you advertise longer prefixes with the same nexthop as the shoter prefix? Is it this use case, or something else? Thanks, Jakob. > -----Original Message----- > From: Russ White [mailto:7ri...@gmail.com] > Sent: Saturday, April 30, 2016 12:35 PM > To: Jakob Heitz (jheitz) <jhe...@cisco.com>; nanog@nanog.org > Subject: RE: Superfluous advertisement (was: Friday's Random Comment) > > > > A use case for a longer prefix with the same nexthop: > > > > F > > / \ > > D E > > | | > > B C > > \ / > > A > > > > Suppose A is a customer of B and C. > > This is possible, but only remotely probable. In the real world, D and E are > likely peered, as are B and C. Further, it's quite possible for F to choose > the path through E anyway, regardless of A's wishes, or even to load share > over to the two paths. If it's really a backup path, and you don't want > traffic on it unless the primary is completely down, then you need to not > advertise it until you actually need it. One of the various principles of > packet based routing is that if you advertise reachability, it means > someone, someplace, might just choose the path you've advertised. You can't > control what other people choose. > > :-) > > Russ
