CCNP Trouble Shooting L3

The following commands can be useful in troubleshooting:

• show ip route ip-address: Displays best route that matches the IP address.
• show ip route network mask: Displays routing table entry that is an exact match for the network and mask.
• show ip route network mask longer-prefixes: Displays routing table prefixes within the network and mask parameters.
• show ip cef ip-address: Displays information necessary to forward packets in the FIB for the prefix (not routing protocol related information).
• show ip cef network mask: Displays the FIB table entry that matches the network and mask.
• show ip cef exact-route source destination: Displays adjacency used to forward a packet with specified source and destination IP addresses.
• show ip arp: Verifies IP address to Ethernet MAC address mappings resolved by ARP.
• show frame-relay map: Lists mappings of next-hop IP addresses on multipoint (sub-) interfaces to the DLCI of the corresponding PVC. It also lists DLCIs manually associated to specific point-to-point sub-interfaces.Virtually all routing protocols include the following elements and processes:
  • Reception of routing information from neighbors
  • Routing protocol data structures
  • Route injection or redistribution
  • Route selection and installation
  • Transmission of routing information to neighbors