Cisco 10000-2P2-2DC Software Guide - Page 318

Monitoring and Maintaining uRPF Chapter 13 Unicast Reverse Path Forwarding Note You can use default route to configure a default path for all addresses that are not in the regular routing table. When configuring uRPF, you can use the allow-default option to allow ip packets with the source address resolved to a valid default path, depending on the uRPF modes. In strict mode uRPF, the packets are allowed from the same interface that has been pointed by the default route. In loose mode uRPF, packets with the source address resolved to the default route are allowed. However, if there is no default route provisioned in the router, the allow-default option on or off would not make any difference regardless of the uRPF mode as there is no valid default path. Monitoring and Maintaining uRPF Unicast RPF counts the number of packets dropped or suppressed because of malformed or forged source addresses. Unicast RPF counts dropped or forwarded packets that include the following global and per-interface information: • Global Unicast RPF drops • Per-interface Unicast RPF drops After you enable uRPF on a router, you can monitor the number of packets getting dropped by the router using the following commands. Command Router# show ip traffic Router# show ip interface type Router# show pxf cpu statistics drop interface Description Displays global router statistics about Unicast RPF drops and suppressed drops. Displays per-interface statistics about Unicast RPF drops and suppressed drops. Displays drop counters by pxf for a given interface, even without uRPF provision and if the interface is not up or does not have an IP address. Caution Because debugging output is assigned high priority in the CPU process, it can render the system unusable. For this reason, use debug commands only to troubleshoot specific problems or during troubleshooting sessions with Cisco Systems technical support personnel. Moreover, it is best to use debug commands during periods of lower network traffic and fewer users. Debugging during these periods decreases the likelihood that increased debug command processing overhead will affect system use. Example 13-1 shows the total number (global count) of dropped packets for all interfaces on the router using the show ip traffic command. The Unicast RPF drop count is included in the IP statistics section. Example 13-1 show ip traffic Command Router# show ip traffic IP statistics: Rcvd: 1753234 total, 1163482 local destination 0 format errors, 0 checksum errors, 0 bad hop count 1162010 unknown protocol, 523362 not a gateway 13-14 Cisco 10000 Series Router Software Configuration Guide OL-2226-23