Number of BGP communities
Purpose
BGP Communities can give a lot of information about a prefix, for example where your BGP peer learned the prefix. As BGP Communities also consume router memory it is suggested to delete the BGP communities if too many of them are attached to a prefix.
Configuration
In Cisco IOS it is not possible to only delete BGP Communities from a prefix when there are more than a specific number attached. You can filter prefixes with eg. >=100 BGP Communities, but then your router won't have a route to the filtered prefix if you do not have a default route.
router bgp 64500
bgp maxcommunity-limit 99
bgp maxextcommunity-limit 99
If you do not want to loose any routes because of too many attached BGP Communities you could also remove all BGP Communities from the prefixes coming from your peer.
ip community-list expanded ALL-COMMUNITIES permit .*
!
route-map BGP_FILTER_IN permit 100
set comm-list ALL-COMMUNITIES delete
set extcomm-list ALL-COMMUNITIES delete
!
router bgp 64500
neighbor 198.51.100.1 route-map BGP_FILTER_IN in
In Cisco IOS XR it is not possible to only delete BGP Communities from a prefix when there are more than a specific number attached. You can filter prefixes with eg. >=100 BGP Communities, but then your router won't have a route to the filtered prefix if you do not have a default route.
router bgp 64500
bgp maxcommunity-limit 99
bgp maxextcommunity-limit 99
If you do not want to loose any routes because of too many attached BGP Communities you could also remove all BGP Communities from the prefixes coming from your peer.
ip community-list expanded ALL-COMMUNITIES permit .*
!
route-map BGP_FILTER_IN permit 100
set comm-list ALL-COMMUNITIES delete
set extcomm-list ALL-COMMUNITIES delete
!
router bgp 64500
neighbor 198.51.100.1 route-map BGP_FILTER_IN in
In this example all BGP Communities are removed from a prefix when >= 100 BGP Communities are attached.
policy-options {
community ALL-COMMUNITIES members [ *:* origin:*:* large:*:*:* ];
policy-statement BGP_FILTER_IN {
term delete-too-many-communities {
from community-count 100 orhigher;
then {
community delete ALL-COMMUNITIES;
}
}
}
In this example all BGP Communities are removed from a prefix when >= 100 BGP Communities are attached.
route-map BGP_FILTER_IN permit 100
match community instances >= 100
set community none
!