Juniper DOS/Blackhole question

Saku Ytti saku at
Sun Oct 23 07:18:58 UTC 2011

On (2011-10-22 20:38 -0500), Jack Bates wrote:

> the route. This seems strange to me. Any idea why a route would be
> rejected unless multihop was enabled?

RFC4271 states:
  - By default (if none of the above conditions apply), the BGP
    speaker SHOULD use the IP address of the interface that the
    speaker uses to establish the BGP connection to peer X in the
    NEXT_HOP attribute.

Your provider was rewriting the next-hop to some address they are blackholing
inside their network. This caused above check to fail, and route was being
considered invalid.

EBGP multihop is kludge to kill this check, but also kludge to kill convergence
of your BGP session, due to disabling fall over on linkdown.

Proper way to disable this check is JunOS 'accept-remote-nexthop' or IOS


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