Setting descriptions on an interface is another administratively helpful thing, and like the hostname, it’s also only locally significant. One case where the description command comes in really handy is when you want to keep track of circuit numbers on a switch or a router’s serial WAN port.
Here’s an example on my switch:
tod # config ttod (config)# int fa0/1
tod (config-if)# description Sales VLAN Trunk Link tod (config-if)# ^Z
And on a router serial WAN:
Router# config t
Router(config)# int s0/0/0
Router(config-if)# description WAN to Miami
You can view an interface’s description with either the show running- config command or the show interface —even with the show interface description command:
tod #sh run
Current configuration : 855 bytes
description Sales VLAN Trunk Link
tod # sh int f0/1
FastEthernet0/1 is up, line protocol is up (connected)
Hardware is Fast Ethernet, address is ecc8.8202.8282 (bia
Description: Sales VLAN Trunk Link
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
tod # sh int description
Interface Status Protocol
Vl1 up up
Fa0/1 up up Sales VLAN
Fa0/2 up up
description: A Helpful Command
Bob, a senior network admin at Acme Corporation in SanFrancisco, has over 50 WAN links to branches throughout the United States and Canada. Whenever an interface goes down, Bob wastes lots of time trying to figure out the circuit number and the phone number of the provider of his ailing WAN link.
This kind of scenario shows just how helpful the interface description command can be. It would save Bob a lot of work because he could use it on his most important switch LAN links to find out exactly where every interface is connected. Bob’s life would also be made a lot easier by adding circuit numbers to each and every WAN interface on his routers, along with the phone number of the responsible provider.
So if Bob had just taken time in advance to preventively add this information to his interfaces, he would have saved himself an
ocean of stress and a ton of precious time when his WAN links inevitably go down!
Doing the do Command
In every previous example so far, we’ve had to run all show commands from privileged mode. But I’ve got great news—beginning with IOS version 12.3, Cisco has finally added a command to the IOS that allows you to view the configuration and statistics from within configuration mode!
In fact, with any IOS, you’d get the following error if you tried to view the configuration from global config:
tod (config)# sh run
% Invalid input detected at '^' marker.
Compare that to the output I get from entering that same command on my router that’s running the 15.0 IOS using the “do” syntax:
tod (config)# do show run
Current configuration : 759 bytes
no service pad
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
So now you can pretty much run any command from any configuration prompt—nice, huh? Looking back through all those examples for encrypting our passwords, you can see that the do command would
definitely have gotten the party started sooner, making this innovation one to celebrate for sure!