IOS: Clearing an Interface Configuration

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.

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