Formula for defining a Subnet Mask

http://www.mindwerks.org/Subneting.htm

Using BGP communities to influence routing

http://evilrouters.net/2009/03/18/using-bgp-communities-to-influence-routing

Networking Fundamentals

http://packetlife.net/blog

BGP Communities

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/15-sy/irg-15-sy-book/irg-named-community-list.html

Routing Protocols timers

http://www.getnetworking.net/cheat-sheets/routing-protocols-timers#comment-258