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Router Security Configuration Guide UNCLASSIFIED 102 UNCLASSIFIED Version 1.0g ingress and egress filtering.  For more details on how and where to apply unicast RPF verification, consult [10]. Configuring Unicast Reverse-Path Verification Unicast RPF verification depends on a particular routing mode called Cisco Express Forwarding (CEF).  Therefore, to use unicast RPF, first enable CEF, and then enable verification on the desired interfaces.  The transcript below shows how to enable verification on the router Central. Central# config t Central(config)# ip cef   Central(config)# interface eth 0/0 Central(config-if)# ip verify unicast reverse-path Central(config-if)# exit Some Cisco routers require you to enable CEF with the command  ip cef distributed  instead of the simple version shown above.   Consult [10] for details about CEF requirements. To disable unicast RPF verification, enter interface configuration mode, as shown above, and use the command  no ip verify unicast reverse-path. 4.4.6.    References [1]    Albritton, J.  Cisco IOS Essentials, McGraw-Hill, 1999. An excellent introduction to basic Cisco IOS tasks.  Portions of this book that are particularly relevant to Routing Protocols are Chapters 2 and 7. [2]    Parkhurst, W.R., Cisco Router OSPF - Design and Implementation Guide,   McGraw-Hill, 1998. Comprehensive and practical guide to OSPF use.  Includes discussion of design issues, security, implementation, and deployment. [3]    Black, U.  IP Routing Protocols, Prentice Hall, 2000. A very good survey of routing protocols and the technologies behind them. [4]    Moy, J.T.  OSPF – Anatomy of an Internet Routing Protocol, Addison-Wesley, 1998. Detailed analysis of OSPF and MOSPF, with lots of practical advice, too.   Includes a good section on troubleshooting. [5]    Thomas, T.M.  OSPF Netwo rk Design Solutions, Cisco Press, 1998. This book offers a good overview of IP routing and related topics, and also explains how to configure Cisco routers for OSPF in a variety of situations.