Multihomed route visibility

We are advertising the same prefix to ISP A & ISP B. When looking at various route servers across the world, I always see the path through ISP A in the BGP table, but most don’t show a path at all through ISP B (some do, like Oregon IX). I would expect any router with the full table to show both routes. Is this a consequence of how the route servers are peered up? Are they only displaying the preferred path? ISP Issue? Am I missing something?

Any help would be appreciated.

Patrick Boyle Data Center Architect / Engineer

Network Solutions Architecture and Engineering Section | Network Technology Services Bureau

SITSD/Montana Department of Administration

406.444.2549 (D)


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Hi Patrick,

Routers only propagate the best BGP route for the target network. You’ll see both only where the AS received different best routes from its peers.

Bill Herrin

You will generally only see the best path. Most route servers don’t collect any backup paths the routers may have, which could be quite extensive.

- Jared