Sunday, March 12, 2006


Inconsistent CLI commands in Cisco IOS.

When I run into IOS commands that seem a bit strange, in most cases when I think about it a bit I can come up with some reasoning for why the commands are the way they are. But sometimes, I run into something that is surely gratuitously inconsistent CLI.

One example is the is-type command under the router isis command mode. If you want the router to be a level-1 router only, you should type in is-type level-1. If you want the router to be a level1/2 router, you should type in is-type level-1-2. So far so good. Now what would you think you need to type in if you want it to be a level-2 only router? I would have expected is-type level-2. However, the command is actually is-type level-2-only as illustrated by the friendly ? below

R1(config-router)#is-type ?
level-1 Act as a station router only
level-1-2 Act as both a station router and an area router
level-2-only Act as an area router only

The help text for the command options consistently uses "only" for both the level-1 only and the level-2 only cases, but the command keyword itself uses "only" for the level-2 case. The good part is that if you were type in just is-type level-2, the router accepts it anyway since level-2 is enough for IOS to know that you mean level-2-only.

This is only a minor glitch but if Cisco were ever to use this on a test with the choices including both level-2 and level-2-only remember this inconsistency or you might lose a point thanks to some Cisco engineer who at least on one day in the distant past gave in to the siren call of the goddess of inconsistency!

I noticed this problem while reading about authentication with eigrp.
You use the key chain name-of-chain command at global configuration and then in the interface configuration you use ip authentication key-chain eigrp as-number name-of-chain.
Wouldn't it be better if it were consistent and both the interface configuration and the global configuration used either the space or the - and not one of each? So much stuff that looks like it could be improved but probably goes ignored.
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