Typical Troubleshooting Commands for Router / Switch

Show controllers Ethernet [interface number] To display statistics like missing datagrams, memory errors, buffer errors, and overflow errors for an Ethernet interface on a Cisco router (Please note this command will not give you information on internal hardware errors)
Show flash To display the router images stored in NVRAM
Show buffers To display statistics for the buffer pools in router (Please note that the router has one pool of queuing elements and five pools of packet buffers of different sizes. Network server keeps counts of the number of buffers outstanding, the number of buffers in the free list, and the maximum number of buffers allowed in the free list for each pool)
Show processes To display information about the active processes in a router
Show tech-support To show tech support router conditions
Show version To show current status of router
Debug ip rip To check if RIP routing is operating properly
Show ip route To display the entries in the routing table
Show version To obtain a router’s firmware version
Show running-config To obtain a router’s current configuration
Show interface fddi 3/0 To display an upstream neighbor value of 0000 0000 0000 for FDDI (Keep in mind that 0000 0000 0000 means the upstream neighbor is unknown, indicating that a physical problem is likely to have occurred)
Debug isdn q921 / debug isdn q931 To troubleshoot ISDN BRI layer 2 and 3
Show controller bri To view information specifically about the D channel of a BRI line
Logging console level To send debugging output to the consol
Show frame-relay To obtain statistics about a PVC (Permanent Virtual Circuit) on all Frame Relay interfaces