Interface is full

This occurs most commonly when you are labbing or testing something and an interface ends up with a lot of configuration, possibly something like the following:

Router(config-if)#do sh run int fa0/0
Building configuration…

Current configuration : 320 bytes
!
interface FastEthernet0/0
description Show the Default command
ip dhcp relay information trusted
ip address 198.18.56.1 255.255.255.0
no ip route-cache cef
no ip route-cache
ip ospf authentication-key MYOHMY
ip ospf network point-to-point
ip ospf hello-interval 20
duplex half
standby 1 ip 198.18.54.90
end

Router(config-if)#

You want to clear this configuration and reuse the interface for some other task. Normally you would need to issue a the “no” command for each line.

The ‘default’ command

The default command has many uses, and this is only one of them, but possibly it is the most useful.

Router(config-if)#default interface fa0/0
Building configuration…

Interface FastEthernet0/0 set to default configuration
Router(config)#do sh run int fa0/0
Building configuration…

Current configuration : 61 bytes
!
interface FastEthernet0/0
no ip address
duplex half
end

Router(config)#

That’s it. Simple and elegant.

Other posts in the series

1. Cisco IOS CLI Regex: sh ip bgp in
2. IOS CLI Tip: More accurate pipe commands
3. Cisco Nexus NXOS and Fixing broken “switchto” syntax with alias
4. show ip eigrp topology all
5. Cisco IOS CLI Shortcuts
6. The poor man's IOS Traffic Generator
7. IOS: "terminal monitor" on, off - logging to your terminal
8. IOS: Console, Terminal, Monitor, VTY - what is what ?
9. IOS: Clearing an interface configuration (This post)
10. IOS: Setting Terminal Window Length
11. IOS CLI: show run linenum
12. IOS: Setting the TCP timeout on IOS
13. IOS: enable and .... disable ?
14. IOS: Reverse SSH console access - Part 2
15. IOS:Open Source Lab DNS and IP addressing
16. IOS: Reverse SSH console access
17. ip tcp timestamp
18. Cisco ASA and IOS command tip - test aaa-server