Running config and Startup config having "differences" post reboot

[sumikum7]

If the startup-config is the first thing applied into running-config then post reload of the device we should see no disparity in contents of "sh start" and "sh run"?

Also, if some CLI went bogus while getting applied to the device post reload stage then will the CLI still remain in startup-config ?

[Seb Rupik]

Hi there,

The config is loaded line by line, and not evaluated as a single unit. Therefore if there are problems with a line of config, the interpreter will throw out an error to the log buffer and just keep processing the remaining config.

cheers,

Seb.

[sumikum7 · Accepted solution]

@Seb Rupik 

Because of this there can be a case where sh run and sh start is different post boot up as those cli which were erroneous in startup config will not be listed in the running config ?

[Seb Rupik · Accepted solution]

Yes. You only tend to end up in these situations if you copied an externally generated file to startup, change system images (different feature sets) or remove/swap linecard/modules.

cheers,

Seb.

[sumikum7]

It seems a different case here. Although I have landed in such situation the reason is not looking anything like this as the CLI can be applied manually!

So, the CLI works but for some reason the same didn't happen when startup config was applied post bootup!

[Seb Rupik]

Do you have the log from boot up? Can you share it?

Which lines of config are having this problem?

[Joseph W. Doherty]

To add to Seb's information, occasionally newer IOSs will slightly change syntax for some commands, but will still recognize the earlier syntax (at least until Cisco decides the prior syntax is so old, they will no longer accept it). This might also apply to entering commands manually, but look for them to be transformed in the running config.

Also, BTW, occasionally, I've seen running configs differ from the startup config, even when the running config has been saved.