I've been having an email discussion with a couple of Cisco engineers about how useful BGP community based IP filtering might be. The following IOS config fragment might help explain what I'm getting at:
int fddi0 ip access-group community-list 10 in ! ip community-list 10 permit AA:BB ip community-list 10 permit CC:DD !
If you are using communities to make your prefix announcements to peers, this then allows the router to filter incoming IP packets that match your announcements. Excepting things like CPU load, implementation details, etc do you think this would be helpful, or am I way off with this?
I think this would be helpful; especially if were scaled as a ubiquitous implementation mechanism. Further implementations of BGP community based decision criteria could include Class of Service/Type of Service Priority Setting; based upon a particular community, give packets with this network source/destination X priority. Additionally, other services such as selective NAT (do or do not NAT based upon communities, NAT into which address space based upon communities), etc... can be implemented. Similar to the regexp niftiness being put into access lists, it'd be keen to see all features using ACLs accept communities as determining factors. Bear in mind this is not terribly useful to the world if Cisco does it alone, it should be tracked through IETF, but it would be nice if Cisco did the proof-of-concept and led the pack. -alan