Cisco config checker

Randy Bush wrote:

of all these cute GUI products, which understands configs used by real ISPs
on real routers with current ISP images? when last i looked, the answer was
the null set.

I can believe that. I've rarely seen any "fancy GUI" software package for
anything that had some real guts under the hood.

I'm planning to put together my own system to build configs from our
customer database (and other stuff). Since it would be a constructed
config, once the code is debugged, I'd tend to trust it (as opposed to
a config manually edited each time). So I would not need something
that merely checks the config for errors.

Now what I could use, is a program (Unix based) that will do the reload
of the configuration smartly, correctly undoing anything that is not in
the new config, such as deleting old static routes, can make the config
go in service without disruptions (reset lines that change, but do not
reset those that do not change, for example), and also save and verify
the saved config. This program would have to know how to get the existing
config and compare the configs to apply the differences. Additional smarts
like knowing not to leave itself without a valid static route (e.g. add
new one before deleting old one) would be great. A "verify only" mode
that simply tells me what would need to be done to make a new config be
in service would also be great.

GUI just gets in the way of real work.