Review my BGP configuration

[Hans van Kranenburg]

On 03/06/2013 02:28 PM, Andre Nathan wrote:
> 
> My router's network interfaces are configured as follows:
> 
>   eth0: interface connected to a.b.0.0/23 network
>   eth1: interface for eBGP and iBGP sessions
> 
> What happened was that my IP block is a.b.0.0/23, and therefore my
> router has an IP address with a /23 netmask in eth0 (say, a.b.0.1/23).
> However, I export two /24 blocks, a.b.0.0/24 and a.b.0.1/24.

I assume you mean to say a.b.1.0/24 instead of a.b.0.1/24?

> The router
> learns these routes from the iBGP session, and since they are more
> specific than the eth0 interface route, they'll be preferred when
> compared to the eth0 interface route.

If there a specific need for advertising the routes you want to send to
your eBGP peer also via iBGP?

> So I ended up with a route to the
> /23 via eth0 and two routes to the /24 blocks via eth1, with the iBGP
> peer as the gateway.

I think you do not want to put the /24 routes in iBGP, because if you'd
do that on both sides, you'd be creating a loop, because afaik traffic
will bounce between them indefinitely and never reach the network on
eth0. :)

> My first thought is that I need another static protocol block in my
> configuration:
> 
> protocol static {
>   route a.b.0.0/24 via "eth0";
>   route a.b.0.1/24 via "eth0";
> }
> 
> Is that a solution to this situation? What's weird to me is that my
> other router (the iBGP peer of the Bird router) is still running Quagga,
> and it learns the same two /24 routes via iBGP but does not add them to
> the kernel routing table. I'm wondering if Quagga is doing some kind of
> filtering here behind the scenes that isn't done by default in Bird...

I'd suggest only using the /24 routes when talking to the peers outside
your network, and use iBGP to only distribute information about routes
originating from outside your AS.

-- 
Hans van Kranenburg - System / Network Engineer
T +31 (0)10 2760434 | hans.van.kranenburg at mendix.com | www.mendix.com