Troubleshooting tehniques

1. using "Show" commands. most commonly used internetwork connectivity testting tools "PING and TRACEROUTE". for debugging, use to help if there any deep problem :D

At the end of every show command there is UNIX like pipe symbol followed

sample
r6#show version | ?
begin
exclude
include

the " begin" option is used to specify a string of characters that will mark where you want to begin viewing lines of the show command

The "include" option is used to identify and display specific lines within a given IOS show command that match a supplied regular expression.

The "exclude" option is used to identify and prevent the display of specific lines within a given IOS show command that match a supplied regular expression.

2. Using the Debugging Tools
  > debug Ip Packet
  > debug Ip Routing

3. Capturing Messages CISCO and Debug Output with SYSLOG
4. Debug Output to a syslog Server
5. Using TCP Dump

Cheat Sheets Part II

Source : packetlife