Re: bgp behavior with exchange prefix in ebgp

[Havard Eidnes <]

I know -- catching up on old e-mail...

> On Fri, Sep 05, 2003 at 10:18:45AM +0200, Iljitsch van Beijnum wrote:
> > Note that the next hop points to an address that falls within the (old) 
> > AMS-IX peering LAN prefix. Since this router isn't directly connected 
> > to the AMS-IX, it needs to resolve this next hop:
>
> Two ways to remedy this:
>
>  - use next-hop-self on all iBGP peerings  (which isn't always the
>    perfect choice, but will easily fix these issues)
>
>  - filter the exchange prefix(es) for all IXes that you participate *and 
>    all more specifics* on *all* eBGP sessions.  This is strongly recommended
>    even when already using next-hop-self (more specifics can break eBGP
>    sessions at the IXP peering routers)

A third and additional defensive measure could be to adjust the
preference of your IGP to a value below that for eBGP, and do the
moral equivalent of "redistribute connected" on the exchange
point router into your IGP.

Regards,

- Håvard