eBGP - iBGP - no-export

[pergranath]

There is an autonomous system network with (at least) three routers (r1, r2 and r3), which run eBGP to different external neighbours (rA, rB and rC) in different AS-numbers.

r1 receives a route for network A.B.C.D via eBGP from rA, and the path is 4 hops.

r2 receives a route for network A.B.C.D via eBGP from rB, and the path is 2 hops and has "no-export" as community.

r3 advertises routes to rC. However, for some reason network A.B.C.D is not advertised to rC.

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Is the above normal behaviour?

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I can add that:

r1 sees both routes to network A.B.C.D, but the "best" route is via rB (with no-export).

r2 and r3 has only one route for network A.B.C.D - the one via rB (with no-export).

------- Question:

Should r3 not see also the route via rA, so that it can advertise that to rC ?

regards,

Per

[Harold Ritter · Accepted solution]

This is normal behavior. BGP selects the best path and only advertises this best path to its peer.

This is the case even if multipath is configured.

Hope this helps,

[pergranath]

I knew that was the case for eBGP, but I thought perhaps it was different for iBGP... it seem it would make sense, but I suppose it does not.

thanks.