Hi Fredy,

On Thu, 7 Jun 2007, Fredy Kuenzler wrote:

I'm building the CDN for Zattoo and as it's some sort of 'anycast' infrastructure (refer to the presentation @ SwiNOG #14), I have several geographically dispersed network islands, not connected via a layer-2 link.

Each network island propagates one or more /24 networks, using AS8302.

Now, BGP mechanism prevents AS-pathes like

^[Transit-AS]_8302$

in my case

^13030_8302$

if I'm AS8302 myself.

I know there is some tweak to prevent this default behaviour. Could anyone give a hint for Foundry and Cisco gear?

you may want to use the "allowas-in" statement in the neighbor configuration (at least on cisco)

allowas-in Accept as-path with my AS present in it

-> neighbor 1.2.3.4 allowas-in

Kind regards, Michael

Fredy Kuenzler wrote:

I'm building the CDN for Zattoo and as it's some sort of 'anycast' infrastructure (refer to the presentation @ SwiNOG #14), I have several geographically dispersed network islands, not connected via a layer-2 link.

Each network island propagates one or more /24 networks, using AS8302.

Now, BGP mechanism prevents AS-pathes like

^[Transit-AS]_8302$

in my case

^13030_8302$

if I'm AS8302 myself.

I know there is some tweak to prevent this default behaviour. Could anyone give a hint for Foundry and Cisco gear?

Normally BGP speakers MUST not be able to disable loop prevention. You're probably thinking of "no bgp enforce-first-as" but that's not relevant here. There was another hack related to network transitions and have two ASs configured at the same time. Though I don't know if this is good enough either.

As an alternative you can have a static route for your entire anycast netblock to one of your upstreams. That fixes the immediate issues but doesn't provide load balancing or failover.