[1] Connectivity and Internetworking Devices by Nortel Networks
[2] Router Protocols,
http://www.control.auc.dk/~obm/graph_theory_f2001/routing/letcture2.html
[3] Chapter 42, Open Shortest Path First (OSPF) by www.cisco.com
[4] Computer Networks and Internets, Douglas Comer, 1999
[5] Routing Information Protocol, www.cisco.com