[c-nsp] eBGP Peer with non-bgp transit router in the middle

[Stephen Wilcox]

Hi William,
 you cant have a router in the middle with less routing information than the routers at the edge because as you say it doesnt know where to send the traffic.

If you dont want/cant run BGP on the transit router then a viable alternative would be to have the transit router have a default to AS-Z-BGP-Router (either static or IGP) then have the transit router learn the routes from AS-Y

Personally, I would run BGP on the transit router and peer directly with AS-Y and drop the multihop config you suggested. Then the transit router can run iBGP with AS-Z-BGP-Router and you can set a route-map on AS-Z-BGP-Router to not announce any prefixes other than a default towards the transit router.

Steve

On Tue, Aug 28, 2007 at 12:52:26PM +0200, William Jackson wrote:
> 
> Hi all
> 
> A recommendation on preferred method of achieving the following
> scenario:
> 
> [AS Y BGP Router]-----------[AS Z transit router]------------[AS Z BGP
> router]
>  
> 
> AS Y router config
> 
> Neighbor BGP-Z-loopback as Z
> 
> Neighbor BGP-Z-loopback ebgp-multihop 10
> 
> Ip route x.x.x.x. 255.255.255.255 y.y.y.y
> 
> AS Z BGP Router
> 
> Neighbor BGP-Y-Interface update-source loopback0
> 
> Neighbor BGP-Y-Interface ebgp-multihop 10
> 
>  
> 
> The BGP neighbors are coming up and advertising routes.
>  
> 
> The problem is that the transit router is only running IGP and has a
> default route passed to it from AS Z BGP router.
> 
> So when its queried about the routes advertised by AS Y it doesn't know
> and simply uses the default thus forming a loop.
> 
>  
> 
> I read that it is recommended to advertise the BGP routes into the IGP
> for this?
> 
> I was planning only using a route-map or some other device to only
> inject into the IGP the routes advertised from AS Y?
> 
>  
> 
> Y is a small AS with three or four routes.
> 
>  
> 
> Any comments?
> 
>  
> 
> thanks
> 
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-- 
Stephen Wilcox
Technical Director, Packetrade Ltd
Tel: +44 (0)845 013 0845
Fax: +44 (0)845 217 8399
AIM/Yahoo: wilco888