BGP summarization

[fmoulineau]

Hello,

What are the best practises to solve this topology

I have several branch offices connected via BGP

to a BGP core Network. Branch office X use

10.X.0.0/16 network

I would like that network core announces summarize

10.0.0.0/8 to each branch offices.

Example:

Branch A (10.1.0.0/16) -- BGP Peer -- BGP Core network -- BGP Peer --Branch B (10.2.0.0/16)

Core network should announce 10.0.0.0/8 to Branch A et B

Thanks.

[jkim]

There are several ways to do this. One is:

router bgp ASN

network 10.0.0.0

then,

ip route 10.0.0.0 255.0.0.0 null0

this will advertise 10.0.0.0/8 to the peers. Then you'll need to add more specific route, the /16's to their respective destination.

John

[mbartell]

In the core network, where the BGP sessions to the branch offices are use the command:

router bgp xxxx

aggregate-address 10.0.0.0 255.0.0.0

You will then want to follow up with applying a prefix-list outbound to your branch offices which will only permit the 10.0.0.0/8 network and will deny the /16's. If you have any other BGP sessions in your core, that are not going to branch offices, you may want to deny the /8 and permit the /16's, or permit both.

The main idea here is to create the network summary, but not to suppress the more specific prefixes. You could also do the following if you do not wish to use the aggregate-address command:

router bgp xxx

network 10.0.0.0

!

ip route 10.0.0.0 255.0.0.0 null0

Same rules apply with respect to filtering routes. If you do not filter the /16's from the branches, there is not much of a reason to generate the /8.

Hope this helps...