Cisco diff – compare configurations

Just a quick post to show how one can compared what is in the startup-configuration
compared to the running-configuration or to compare to different configurations
stored on flash on Cisco devices.

The device boots up with the startup-configuration. Then we add some commands to
the running-configuration but we do not save them.

R1(config)#int f0/0
R1(config-if)#ip add 192.168.0.1 255.255.255.0
R1(config-if)#no shut
R1(config-if)#description link to Datacenter
R1(config-if)#ip route 192.168.2.0 255.255.255.0 192.168.0.2

Then the show archive command is used to show what’s different between the two versions.

R1#show archive config differences
Contextual Config Diffs:
interface FastEthernet0/0
 +no ip address
 +shutdown
interface FastEthernet0/0
 -description link to Datacenter
 -ip address 192.168.0.1 255.255.255.0
-ip route 192.168.2.0 255.255.255.0 192.168.0.2

Commands with a + sign in front of it are present in the startup-configuration but
not in the running-configuration. If there is a – sign then they are present in the
running-configuration but not in startup-configuration.

It is also possible to compare a file stored in NVRAM to the running-configuration.

R1#dir flash:
Directory of flash:/

    1  -rw-         967                      config.old

16777212 bytes total (16776180 bytes free)

R1(config)#int f0/1
R1(config-if)#ip add 10.0.0.1 255.255.255.0
R1(config-if)#no shut
R1(config-if)#description to Firewall
R1#show archive config differences system:running-config flash:config.old
Contextual Config Diffs:
interface FastEthernet0/1
 +no ip address
 +shutdown
interface FastEthernet0/1
 -description to Firewall
 -ip address 10.0.0.1 255.255.255.0

Just a little tool that may be helpful to see what is different between versions. It
could be used for such things as editing an ACL by uploading a file to the device.
Then do a diff between the files to see what is changing in the ACL.