[c-nsp] BGP - Announcing routes to Internet providers.

Jared Mauch jared at puck.nether.net
Mon Jan 4 15:42:08 EST 2010


On Jan 4, 2010, at 3:35 PM, Drew Weaver wrote:

> Howdy,
> 
> I am trying to figure out if there is a different/newer/better(?) way to announce our public IP ranges to our Internet providers, currently we are declaring our subnets in 'network statements' in the BGP configuration, we have static routes setup like ip route x.x.x.x 255.255.224.0 Null0 254 and then we have a extended access-list applied to each peer with our net blocks listed in them.
> 
> It appears that because of the network statements, the supernet routes (/18s, /19s, etc) are being distributed via BGP to the rest of the network which is by design(I assume). This doesn't seem ideal because if traffic is sent to an IP address that doesn't have a more specific route than say /18, or /19 it travels all the way through the network to the edge before stopping. I might be blowing the impact of this out of proportion, but it just seems like a waste of resources.
> 
> Does anyone know of a seemingly more sensible way of doing this?


You could always tag these hold-down routes with a community, then when someone sends a packet to them, the next-hop could be rewritten to a local discard/null0 instance.

This should allow you to distribute the load instead of backhauling the traffic to the final destination/aggregation location.

- Jared



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