[c-nsp] BGP question

[Danny McPherson]

On Sep 21, 2004, at 9:44 AM, James Hampton wrote:

> I am seeing some unexpected behavior. I have 2 boarder routers each
> are IBGP together and EBGP with there perspective providers. On br2 I
> have a prefix list with all our internal prefixes going out and
> another filtering bogons in, so far so good. But I currently only have
> 1 network statement with one prefix advertised so I can test the link
> on br2. All was good when I checked the providers route server I only
> saw the 1 network I was advertising. Than when I brought up IBGP
> between the two boarder routers and suddenly all our internal prefixes
> were learned by the provider on br2 even though I was only explicitly
> advertising 1 network via the network statement. Does a router
> automatically advertise prefixes learned from an IBGP peer to a EBGP
> peer?

Yes, if no policy is otherwise specified to prohibit this
behavior.  I suspect you need to add an outbound filter
on br2 to the EBGP peer to permit only the one prefix.
Otherwise, permit all your prefixes since you've evidently
now tested the link :-)

-danny