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!


Discontiguous address ranges in a NAT pool. (Question #38)

Consider the situation where you want to use the addresses
in a NAT pool with the constraint that the subrange starting from the
address and ending with the address not be used
for NAT translations. How would you accomplish the task?

This page is powered by Blogger. Isn't yours?