Majorbacon's Quick Important Shortcuts for the Cisco CLI

I wanted to share four things that speed up my use of the Cisco CLI.

The first three tricks are associated with register context. In order to perform command you have to enter the correct context first. Global, Global Configuration, Specific Configuration (like VLAN, Router, Interface, Line, etc.) Sometimes being in the wrong context slows you down, and these tricks help speed you back up again.

1) Get Global

If you are in a sub-interface level command, you can enter a different sub-interface without returning to the parent interface.

For example:

(config)# interface fa 0/0
(config-if)# ip address 192.168.1.1 255.255.255.0
(config-if)# interface fa 0/1
(config-if)# ip address 192.168.2.1 255.255.255.0

 - notice that there was no exit command between the second and third steps.

Another way to avoid the exit in a sub-interface mode is to type a global configuration command without exiting first - really that's what you did a moment ago - you called for a global config command to enter a sub-interface without leaving the interface first. But you can enter any global config command you want!

For example:

(config)# interface fa 0/0
(config-if)# ip address 192.168.1.1 255.255.255.0
(config-if)# hostname Router1
(config)#

 - Notice that the router rip command, a global configuration was issued without leaving the sub-interface context, and then I was left at the global level. Be aware that tab-completion and ? help will not work across contexts.

2) Do the "Do"

If you are in any configuration mode and wish to issue a command from the enable mode, such as all the show and debug commands, you can do so with the "Do" command. You remain in your config mode, but get the results from the enable mode.

(config)# interface fa 0/0
(config-if)# ip address 192.168.1.1 255.255.255.0
(config-if)# no shutdown
(config-if)# do show ip int briefInterface  IP-Address    OK?  Method    Status       Protocol
S0          unassigned   YES  unset     admin down    down
Fa0/0      192.168.1.1   YES  unset     up             up
(config-if)#

-notice that with the do command I was able to verify what I had done at the interface level, saving myself from typing the exit command, the configure terminal command, and the interface fa 0/0 command!

3) Sanity Check!

Translating "undegub"... domain server (255.255.255.255)

One of the more annoying behaviors on a Cisco device is when you completely fat-finger it and then the entire device pauses for a good minute as though to punish you for your error with a strange 255.255.255.255 message.

This also can happen when you are in the wrong context and it doesn't recognize your command there.

This is because by default, when you enter an unrecognized command the router believes that this must be a host name of a device you want to telnet to! Assuming you haven't defined a DNS server in the configuration the router will issue a broadcast for the command to be translated into an IP address. Waiting for broadcasts to fail takes several seconds for the router. (Waiting for broadcasts to fail has been the bane of administrators since the dawn of time).

The fixes: 

1. Skip attempting look-ups altogether (you'll have to use the local hosts table if you want name resolution)
   (config)# no ip domain-lookup
2. Or point to a valid dns server but disable dynamic lookup
   (config)# ip name-server 8.8.8.8
   (config)# line vty 0 15
   (config-line)# transport preferred none

 

4) Where do I "begin"?

When you show a long list, such as a mac-address-table or configuration file, it is often inconvenient to try and  find the particular place where an item is located that you want to verify. Fortunately, you can pipe your show command into a begin statement that will actually find what you are looking for and start your results there!

For example:

Router1# show running-config | begin line
Building configuration...
line con 0
  transport input none
line aux 0
line vty 0 15
!
no scheduler allocate
end

So - I hope these tools will help you use Cisco's CLI with greater speed and agility, so you can spend less time scanning and more time doing!