Hi, To save some IP space, we are playing a lot with /32 routes, which sometimes leads to unusual network setups.
Specifically, we've hit this issue with Bird: http://marc.info/?l=bird-users&m=133465758907527&w=2 Basically, bird refuses to import a route from the kernel if the next-hop is not in a directly connected network. For instance, with a routing table like this: XX.XX.XX.32 dev eth1.101 proto static scope link src XX.XX.XX.1 XX.XX.XX.64/28 via 91.216.110.32 dev eth1.101 proto static bird will import the first route, but not the second one, spamming logs with "KRT: Received route XX.XX.XX.64/28 with strange next-hop XX.XX.XX.32". This is probably a good idea in most cases, but there are setups where these kind of routes make sense. The workaround described in the above thread ("ip addr add XX.XX.XX.1 peer XX.XX.XX.32") does not always apply, since we may want to have multiple /32 peers directly reachable on a given interface. We found another workaround (note the "onlink" flag and the "via" part): ip route add XX.XX.XX.32/32 via XX.XX.XX.32 dev eth1.101 onlink proto static This basically tells the kernel that the route we added is indeed in a connected network, so that Bird is happy. Note that subsequent routes using this /32 as next-hop also need the "onlink" flag: ip route add XX.XX.XX.64/28 via XX.XX.XX.32 dev eth1.101 proto static onlink In the hope that it will help someone someday, Baptiste
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