3.3 Troubleshooting Routing Protocols  
  3.3.2 Troubleshooting RIP configuration  
The most common problem found in Routing Information Protocol (RIP) that prevents RIP routes from being advertised is the variable-length subnet mask (VLSM). This is because RIP Version 1 does not support VLSM. If the RIP routes are not being advertised, check the following:
  • Layer 1 or Layer 2 connectivity issues exist.
  • VLSM subnetting is configured. VLSM subnetting cannot be used with RIP v1.
  • Mismatched RIP v1 and RIP v2 routing configurations exist.
  • Network statements are missing or incorrectly assigned.
  • The outgoing interface is down.
  • The advertised network interface is down.

The show ip protocols command provides information about the parameters and current state of the active routing protocol process. RIP sends updates to the interfaces in the specified networks. If interface FastEthernet 0/1 was configured but the network was not added to RIP routing, no updates would be sent out or received from the interface.

Use the debug ip rip EXEC command to display information on RIP routing transactions. The no debug ip rip, no debug all, or undebug all commands will turn off all debugging.

Figure shows that the router being debugged has received an update from another router at source address 192.168.3.1. That router sent information about two destinations in the routing table update. The router being debugged also sent updates. Both routers broadcasted address 255.255.255.255 as the destination. The number in parentheses is the source address encapsulated into the IP header.

An entry most likely caused by a malformed packet from the transmitter is shown in the following output:

RIP: bad version 128 from 160.89.80.43

 

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