Computer Certification

As a CCNA or CCNP
one thing you've got to get used to is that change is constant. Cisco regularly issues new IOS versions
not to mention the many different kinds of hardware they produce! While it's always nice to have "the latest and the greatest" when it comes to routers
switches
firewalls
etc.
we have to be prepared for the fact that not all our clients are going to have that latest and greatest!

For instance
there are still quite a few Catalyst 5000 switches out there humming away
and if you're used to working on IOS-driven switches like the 2950
the same command can have dramatically different results.

Let's say you're going to examine the spanning tree protocol (STP) setup of a new client. You're used to working with newer 2950 switches
and you've always run show span on those switches to display spanning-tree information. Then
you run show span on a Catalyst 5000 - and something like this shows:

switch (enable) show span

Destination : Port 6/1

Admin Source : Port 6/2

Oper Source : Port 6/2

Direction : transmit/receive

Incoming Packets: disabled

Learning : enabled

Multicast : enabled

Filter : -

Status : active

Total local span sessions: 1

What's going on here?

The command show span on a 5000 will not show spanning tree stats - instead
what you're going to see are statistics relating to Switched Port ANalyzer (SPAN). Surprise!

Consider an example where you're used to running show span on 5000 switches to see SPAN information. When you run that on a 2950
you know now what you're going to get - spanning tree information! On a 2950
you'll need to run show monitor session
followed by the SPAN session number.

SW1#show monitor session 1

Session 1

---------

Type : Local Session

Source Ports :

Both : Fa0/1

Destination Ports : Fa0/2

Encapsulation : Native

Ingress: Disabled

As a CCNA and CCNP
this is one of those things you just have to get used to. Commands are going to be different
sometimes radically so
between models. That's why you need to be adept with both IOS Help and Cisco's online documentation site. IOS Help is easy
but the online doc site take a little getting used to. Once you learn how to navigate that site
a world of Cisco knowledge is at your fingertips.

Besides
when you sit for the CCIE lab exam
that will be the only friend you have! And a valuable friend it can be - you're just going to have to trust me on that one. :)