Bambang F. Indarto

The Journey… The Shares

Most Useful “Show” Commands in Cisco Router

Posted by bfindarto on March 12, 2008

Show command in cisco routers is the most important and useful tools to see (mostly) recent router’s configuration. Here are about ten show commands that widely used…

  1. show version
    This command shows detailed information about the IOS. It shows the file name of the IOS along with the version of the IOS and value of the configuration register. The configuration register is a set of bits that controls the boot sequence of the router. This command is the only command used to show this register’s value.
  2. show running-config
    This command is your true best friend. It shows the complete configuration that is running currently. Using it you can troubleshoot almost all issues regarding routing, filtering, secure access, and many other issues. Using it before you start configuring the router would give you a clear idea of what services and protocols are operating by default and which are turned off by default.
  3. show startup-config
    This command shows the configuration that is saved on the NVRAM. It is helpful in knowing the configuration that will be applied the next time the routers is reloaded. And also this command is useful in knowing the configuration that was loaded at the start-up of the router before making changes to it.
  4. show ip interface <brief>
    This command displays information about IP protocol and the interface, and if you type “brief”, means show the information briefly. You might be wondering why would you need this command. I will answer that. This command shows which access-lists are applied at the interfaces and in which direction. This kind of information is not shown by the ‘show access-list’ command. However, you can find out which access-list is applied where using ‘show run’.
  5. show interfaces
    This command shows status and statistics regarding interfaces. This command is almost always needed in troubleshooting routing and link issues. Things that are shown using this command include, interface IP address and subnet mask, interface status, encapsulation type, bandwidth, and many other important indicator about the interface operation.
  6. show ip route
    This command shows the routing table. This table helps you in finding out the next hop for each and every routable packet. It is the first indicator to point a problem in routing.
  7. show ip protocols
    This command shows the routing protocols used in the router and what networks are these protocols advertising. It also shows the sources of routing updates received at this router. It is very useful in routing issues troubleshooting.
  8. show access-list
    This command shows the contents of each access-list. It is very useful in troubleshooting filtering issues. Note that this command does not show you where each access-list is applied. 
  9. show cdp neighbor detail
    This command displays detailed information about the neighboring devices like IP addresses, platforms, and host names. This command can be useful in troubleshooting connectivity issues, and also can be used in finding out how devices are connected to each other when you have no clear drawn network map. 
  10. show flash or show slot0
    This command is used to view the contents of the flash and the size of the IOS file(s) and the size of the flash and how much of it is free. It is necessary in upgrading or installing the IOS file.
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