nanog mailing list archives

Re: BGP next-hop


From: Brett Watson <brett () the-watsons org>
Date: Thu, 30 Sep 2010 17:01:11 -0700


On Sep 30, 2010, at 4:57 PM, Randy Bush wrote:

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.

Neither do I, Randy.

a good friend at cisco says he will take the time to write up why in the
next day or two.

Only thing I can guess from the Cisco doc that says:

"To prevent the creation of loops through oscillating routes, the multihop will not be established if the only route to 
the multihop peer is the default route (0.0.0.0)."

Is that they think they're saving you from shooting yourself in the foot, if you learn the route to 147.28.0.0/16 via 
BGP (which your multihop peer address falls in), yet you have a default route of 0.0.0.0? But then you'd simply 
recursively look up the FIB route to the next hop in BGP... so I still don't get it.

-b

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