[ due to my misunderstanding of mailing lists, the end of the discussion went offline. I copy here for other people / traceback ] Hi, Olivier! On 2015-03-10 14:46, olivier a wrote: I retried with 2 routers inline : 192.168.4.0/24---[R1]---192.168.1.0/24-[BIRD]----192.168.5.0/24 Shouldn't 192.168.1.0/24 be not announced or announced with metric infinity on the 192.168.1.0/24 network ? No :-) The network 192.168.1.0/24 is directly connected network to the [BIRD] router and it knows this route from the bird.conf configuration ('proto static' or 'proto direct'). Split-horizon rule is applied in update message only for routes that are sending to the router from which the [BIRD] router was this routes learned. BIRD routing table : ------------------------------------------------------------------- $ ip -4 route show default via 192.168.1.1 dev eth0 proto static 192.168.1.0/24 [2] dev eth0 proto kernel scope link src 192.168.1.240 metric 1 192.168.4.0/24 [3] via 192.168.1.230 dev eth0 proto bird 192.168.5.0/24 [4] dev eth1 proto kernel scope link src 192.168.5.1 metric 1 ------------------------------------------------------------------- BIRD announces on the 192.168.5.0/24 network : 0.0.0.0 Metric 1 192.168.1.0 Metric 1 192.168.4.0 Metric 2 192.168.5.0 Metric 1 BIRD announces on the 192.168.1.0/24 network : 0.0.0.0 Metric 1 192.168.1.0 Metric 1 192.168.4.0 Metric 16 Here (192.168.4.0 Metric 16) we see a split-horizon usage. Becouse we are sending a update to 192.168.1.0/24 network from which we learned about the network 192.168.4.0. 192.168.5.0 Metric 1 Okay? :-) Yours Truly, Pavel