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Ways to use lists in IP route filtering for BGP, with generic command examples
Path filters
ip as-path access-list <aslist1> ...
... permit <reg-ex>
... deny <reg-ex>
... permit <reg-ex>
ip as-path access-list <aslist2> ...
... permit <reg-ex>
... deny <reg-ex>
Prefix filters
ip prefix-list <plist1> ...
... permit x.x.x.x/24
... deny x.x.x.x/24
ip prefix-list <plist2> ...
... permit x.x.x.x/24
... deny x.x.x.x/24
Community
lists
ip community-list <clist1> ...
... deny internet
... permit noexport
Entities in the column above are
the possible lists that can be a part
of per-peer BGP filtering. These lists
can be applied directly to a BGP
peer (except for community lists) or
added to a route map (middle
column), which is then added to a
BGP peer (last column).
Route maps
route-map <map2> deny 1
match as-path <alist2>
route-map <map3> permit 1
match ip address prefix-list <plist2>
ip route-map <map4> permit 1
match community <clist1>
set comm-list <clist1> delete
route-map <map1> permit 1
match ip address 1
bgp neighbor x.x.x.x prefix-list <plist1> in
bgp neighbor x.x.x.x filter-list <alist2> out
bgp neighbor x.x.x.x filter-list <alist1> in
bgp neighbor x.x.x.x prefix-list <plist2> out
bgp neighbor x.x.x.x route-map <map4> out
bgp neighbor x.x.x.x route-map <map1> out
bgp neighbor x.x.x.x route-map <map3> in
bgp neighbor x.x.x.x route-map <map2> in
ACLs
access-list 1 deny x.x.x.x 0.0.0.255
bgp neighbor x.x.x.x distribute-list 1 in