BGP route back

Roman Romanyak roman.romanyak at
Fri Jan 18 19:14:47 CET 2019

Hello Bird users,

Does anyone know if there is a way to announce a BGP route back to the
router it was received from.
I need to do this for the following scenario.
Lets say there are two routers with 2 transit links on each with full view
tables and Bird server as a route-reflector. There is a need to force
traffic to a specific destination via one of the ISPs, so I match the route
in the import filter  and set a local pref on it. But that will only make
the route server announce the route with a high local pref to a second
router, where the desired transit isn't directly connected. So I get the
desired effect on the second router, it will learn and install a route with
high local pref. The first router where the desired transit link is
connected by default selects another transit link because of the shorter

Here is the import filter snippet (x.y.z.0/24 is a dest route, as-path 1234
is a directly connected ISP on router-1:

        if source = RTS_BGP && net = x.y.z.0/24 && bgp_path.first = 1234
then {
            bgp_local_pref = 150;

I think that bird doesn't do that because the protocol matches on the peer
and on the route.

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