Recovery options for running-config Cisco ASA (running IOS 8.2)

cisco-asa

We're setting up an ipsec tunnel and as I look at the config to apply, I'm not really comfortable with how to rollback our changes.

I'm familiar with saving the config in this manner:

copy running-config startup-config

I'm familiar with loading config in the opposite way:

copy startup-config running-config

However I understand that last command will do more a merge of the previous config than overwriting, and isn't a guarantee of restored values.

The only sure-fire method I know of would be to run a reload, which would wipe the running-config and load entirely from startup-config on the reboot, but that would then make interruption of network traffic certain, perhaps taking some minutes.

Is there another way to recover the config more dependably?

I found a command called configure replace, which looks promising, but it doesn't look as if I have it on my ASA: 

ciscoasa(config)# configure ?

configure mode commands/options:
  WORD             Configure from HTTP:
                   http(s)://[<user>:<password>@]<location>[:<port>]/<pathname>.
                   Place IPv6 address within square brackets if a port is
                   specified. 
  factory-default  Configure from factory-default
  memory           Configure from memory
  net              Configure from tftp

exec mode commands/options:
  terminal  Configure using terminal/console

Best Answer

Indeed copy startup-config running-config will do a merge, not an overwrite. So you can do the following:

clear config all

copy startup-config running-config

Obviously this will still cause a brief outage as there is a (very short) timeframe during which the ASA operates with the default config, but it should definitely be shorter than rebooting.

Just make sure to do this on the console, if you do it over SSH you could cut yourself off.

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