How to deny access to a specific network for specific AS?

Question

Computer networks

Hi all!
Question such - Is a network with 4 AS, (AS1, AS2, AS3 and AS4). My AS4 has 3 networks, let's say network 1, 2, 3, how to make network 3 not available in AS1 and AS2? Settings can only be made on the router in AS4.

Answer 1

It's easier - to ask the AS3 admin not to announce the route to this network to others, a little more difficult - to agree on a community in which prefixes will come without announcing to others and give the AS3 route to this network with this community.
In peering with AS1/AS2, add this network to the return filter
Read more xgu.ru/wiki/BGP_community

Answer 2

it's easy to filter. choose a typical task
as convenient
neighbor 2 distribute-list xxx out
neighbor 2 prefix-list yyy out
neighbor 2 route-map zzz out
well, or for a junik
policy statement bgp-export term 1 from route-filter 3 reject