Brad Edgeworth, Aaron Foss & Ramiro Garza Rios (2014). IP Routing on Cisco IOS, IOS XE, and IOS XR: An Essential Guide to Understanding and Implementing IP Routing Protocols. Cisco Press. p. 2. ISBN9780133846768.
Gary A. Donahue (2011). Network Warrior: Everything You Need to Know That Wasn't on the CCNA Exam. O'Reilly Media. p. 10. ISBN9781449309350.
Gary A. Donahue (2011). Network Warrior: Everything You Need to Know That Wasn't on the CCNA Exam. O'Reilly Media. p. 222. ISBN 9781449309350.