Cisco config checker

S.J.Brannon steve at
Tue Jan 5 17:47:05 UTC 1999

One other problem with the Cisco config is that you can not see the FULL config.
Only the differences from the defaults.
I have had a number of problems where option defaults have changed from one release to another.
I is not possible to move a config from on software version to another (no new features used)
and it guaranty to work.
I can remember a problem with Apple Talk address gleaning.
It was off by default in the old software but on by default in the new.

It is not possible to see this by looking at the running config in either router.

I would like to be able to get a FULL config from a router if only for reference.

From: 	Phil Howard[SMTP:phil at]
Sent: 	Monday, January 04, 1999 13:17
To: 	S.J.Brannon
Cc: 	lad at; nanog at
Subject: 	Re: Cisco config checker

S.J.Brannon wrote:

> We have suggest to Cisco that if this tool is to be usable it must be in step with the IOS releases and regression tested.

IOS has inside a data representation of what it things the configuration
is (or should be).  It read it in and it can write it back out.  It is
that internal data structure, as complex and messy as it probably is,
having parts of the data scattered in so many modules, that really could
represent the delta.  Perhaps the only reliable way to do this is to do
it inside IOS itself.  With a new semantic of a config load that would
mean "replace the old config entirely with this config" (as opposed to
the existing semantic "merge this config with the old config") and the
IOS would do the right thing, this might work.  It would be a little bit
more black magic, but it would beat having to keep two different IOS
config interpreters in sync (the real IOS and the external tools).

> This tool can never tell if the real network will work

I don't think this problem will ever be truly solved by any means other
than the ones we use now (check it the best you can, have a fallback
plan, and go for it at a time of least disruption).

 --    *-----------------------------*      Phil Howard KA9WGN       *    --
  --   | Inturnet, Inc.              | Director of Internet Services |   --
   --  | Business Internet Solutions |       eng at        |  --
    -- *-----------------------------*      philh at       * --

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