For 20 years in the industry, I’ve misunderstood an element of BGP. My understanding was that “multihop” was used any time you might receive a route from a thing, but be given destinations for other things. In some cases, that mean routers multiple hops away, yes. But in my incorrect understanding, it also meant route-servers at Internet Exchanges (which are considered directly connected. So for all of my time at this job and last, I set nearly everything in Quagga/zebra/BIRD to multihop…and it worked. But…recently something in Linux changed, it seems…where the algorithm used to recursively try to solve routes when “multihop” was used now completely ignores directly-connected interfaces, maybe...? So…when BIRD did it’s reconfig…all of a sudden it was unable to resolve the route lookups for anything labeled “multihop”. This resulted in every route received over a multihop BGP session with a route-server at an IXP being marked "!", unreachable, reject. Thus, removing the line “multihop” from all of our route-server peers fixed the issue, routes were again received and added to the kernel properly, and life went on. Maybe nobody else out there has the same misunderstanding I did, and nobody will ever experience this again...but if posting here in my embarrassment helps one of you down the line, I suppose it was all worth it. -jake