We use large BGP communities for both informational and alterable communities.
Informational
These communities are available on both ix/peer and customer/downstream prefixes.
Location, type, … information
Community
Description
MY_ASN:100:1
Originated by MY_NETWORK
MY_ASN:100:2
Learned from customer/downstream
MY_ASN:100:3
Learned from Direct Peer
MY_ASN:100:4
Learned from IX route servers
MY_ASN:100:5
Learned from transit/upstream
MY_ASN:101:SESSION_ASN
Learned from SESSION_NAME
MY_ASN:102:IX_ASN
Learned from Internet Exchange IX_NAME
MY_ASN:103:ROUTER_COUNTRY_CODE
Learned in Country ROUTER_COUNTRY_NAME
MY_ASN:104:ROUTER_LOCATION_ID
Learned in Location/Datacenter ROUTER_LOCATION_NAME
MY_ASN:105:ROUTER_ID
Learned from ROUTER_NAME
Validation information
Community
Description
MY_ASN:510:1
Validated IPv4 customer/downstream route
MY_ASN:510:2
Validated IPv6 customer/downstream route
MY_ASN:520:1
RPKI validated customer/downstream route with state valid
MY_ASN:520:2
RPKI validated customer/downstream route with state not found
MY_ASN:520:3
RPKI validated customer/downstream route with state invalid
MY_ASN:530:1
prefix too long (smaller < 7 for IPv4 or < 12 for IPv6)
MY_ASN:530:2
prefix too small (greater > 24 for IPv4 or > 48 for IPv6)
MY_ASN:540:1
Validated Bogon AS filtering
MY_ASN:540:2
Validated Bogon prefix filtering
MY_ASN:550:1
Validated Long AS path filtering
Alterable / Actions
When these communities are applied to prefixes received by MY_NETWORK they alter their routing policy in our autonomous system. They are available only on customer/downstream BGP sessions.
Blackhole
Community
Description
65535:666
Blackhole
MY_ASN:0:666
Blackhole
Routes tagged with the blackhole community must be either an IPv4 /32 or an IPV6 /128 and have an encompassing IRR route or route6 object from an authenticated source like ARIN, APNIC, AFRINIC, or RIPE.
Well-known Communities (RFC)
Community
Description
65535:0
Gracefull shutdown, lowers local-pref to 0
65535:65281
No Export (RFC1997)
65535:65282
No Advertisement (RFC1997)
65535:65284
No Export (RFC3765)
Prepend
Community
Description
MY_ASN:600:1
Prepend the peer AS one time
MY_ASN:600:2
Prepend the peer AS two time
MY_ASN:600:3
Prepend the peer AS three time
MY_ASN:601:n
Prepend the peer AS one time to AS[n]
MY_ASN:602:n
Prepend the peer AS two time to AS[n]
MY_ASN:603:n
Prepend the peer AS three time to AS[n]
Local preference
Community
Description
MY_ASN:610:x
Set local preference to [x]
By default, MY_NETWORK customers/downstreams are imported to BGP with LocalPref 5000. However, MY_NETWORK provides a LocalPref manipulation community that will allow you to control the link over which traffic comes in for active-passive backup purposes. You can set the LocalPref to 4000 by tagging the route with MY_ASN:610:4000, which is still higher than non-customer routes.