BGP route back

Ondrej Zajicek santiago at
Tue Jan 22 15:38:15 CET 2019

On Fri, Jan 18, 2019 at 01:14:47PM -0500, Roman Romanyak wrote:
> 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.


I recently thought about a setup where a route-reflector modifies routes
and propagates modified routes to its clients. To avoid issue with
announcing route back and with (like you noticed) and with withdrawing
original route (like Alexander Zubkov noticed) there is a simple solution:

Use two RIB routing tables on clients and two single-directional BGP
sessions - first RIB table collects routes from EBGP peers and uses first
BGP session to propagate that to route-reflector, then second BGP session
is used to propagate all routes back from route-reflector to second table
in clients, while second table is connected to kernel/FIB.

Such setup could be done in BIRD, i am just wondering whether client part
of such setup could be done with common L3 switches with BGP support.

Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3,
"To err is human -- to blame it on a computer is even more so."

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