North American Network Operators Group
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Re: weird BGP cisco-ism? [problem resolved]

  • From: Dorian R. Kim
  • Date: Fri Jul 11 23:28:03 1997 
On Fri, 11 Jul 1997, Robert Gutierrez wrote:

> I hate to state the obvious, but don't you filter your own blocks from
> your other BGP peers?  Inbound, I mean.  Very simple:

> Isn't this akin to wearing a condom nowadays in the 'net BGP routing
> warz.

Depends. Consider the following scenario:

You have a customer X that is dual homed to provider A and provider B. X is
numbered out of provider A's CIDR block. If the connection between X and
provider A drops, and provider A filters A's own blocks, then while the
connections remains lost, there is no connectivity between X and A.

So simply filtering one's own blocks from peers can cause problems. The most
rational thing to do is to block all except the specifics of dual homed
customers, but whether one does that or not depends on level of configuration
automation one has achieved, I think.

-dorian