[j-nsp] BGP Route Reflector

[Jesper Skriver]

On Mon, Apr 21, 2003 at 05:11:07PM +0800, Tay Chee Yong wrote:
> Hi all,
> 
> I have 2 route reflectors (Router A and Router B).
> 2 RR clients (C and D)
> 
> Both C and D are the clients of A and B
> A and B are full mesh
> 
> Both A and B are using the same cluster id, 1.1.1.1
> 
> I then add router E to be client of B only, with some routes filtering.
> 
> Strangely, router A is not selecting the better route from B learned from
> E, instead router A is registering the better route from its learned eBGP
> peer.
> 
> Why aren't B propagating the better route learned from E to router A?

A router reflector will discard all routes learned with it's own cluster
id, see rfc2796 section 7, which say

   CLUSTER_LIST

   Cluster-list is a new optional, non-transitive BGP attribute of Type
   code 10. It is a sequence of CLUSTER_ID values representing the
   reflection path that the route has passed. It is encoded as follows:

             0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Attr. Flags  |Attr. Type Code|   Length      | value ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where Length is the number of octets.

   When a RR reflects a route, it must prepend the local CLUSTER_ID to
   the CLUSTER_LIST.  If the CLUSTER_LIST is empty, it must create a new
   one. Using this attribute an RR can identify if the routing
   information is looped back to the same cluster due to mis-
   configuration. If the local CLUSTER_ID is found in the cluster-list,
   the advertisement received should be ignored.

/Jesper

-- 
Jesper Skriver, jesper(at)skriver(dot)dk  -  CCIE #5456

One Unix to rule them all, One Resolver to find them,
One IP to bring them all and in the zone to bind them.