BGP next-hop

Thu Sep 30 22:00:08 UTC 2010

Because the path was broken everytime the bgp session was established and rewriting the routing table with more specific routes?

----- Original Message -----
From: "Randy Bush" <randy at psg.com>
To: "North American Network Operators Group" <nanog at nanog.org>
Sent: Thursday, 30 September, 2010 2:37:43 PM
Subject: Re: BGP next-hop

i was recently bitten by a cousin of this

research router getting an ebgp multi-hop full feed from 147.28.0.1
(address is relevant)

it is on a lan with a default gateway 42.666.77.11 (address not
relevant), so it has

    ip route 0.0.0.0  0.0.0.0  42.666.77.11

massive flapping results.  

it seems it gets the bgp route for 147.28.0.0/16 and then can not
resolve the next hop.  it would not recurse to the default exit.

of course it was solved by

    ip route 147.28.0.0  255.255.0.0  42.666.77.11

but i do not really understand in my heart why i needed to do this.

randy