BGP Community Lists

There are two types of community list. One is standard community list and another is expanded community list. Standard community list defines communities attribute. Expanded community list defines communities attribute string with regular expression. Standard community list is compiled into binary format when user define it. Standard community list will be directly compared to BGP communities attribute in BGP updates. Therefore the comparison is faster than expanded community list.

http://www.quagga.net/docs/docs-multi/BGP-Community-Lists.html
http://www.quagga.net/docs/docs-multi/BGP-Extended-Community-Lists.html
http://www.cisco.com/en/US/docs/ios/12_3t/ip_route/command/reference/ip2_s1gt.html
http://www.cisco.com/en/US/docs/ios/12_3t/12_3t11/feature/guide/gtnextcl.html#wp1050903