Cisco CCNA / CCNP Certification Exam: Same Command, Different Results

Writen by Chris Bryant

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.

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of free CCNA and CCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.

You can also join his RSS feed and visit his blog, which is updated several times daily with new Cisco certification articles, free tutorials, and daily CCNA / CCNP exam questions! Details are on the website.

For a FREE copy of his latest e-books, “How To Pass The CCNA” and “How To Pass The CCNP”, visit the website and download your free copies. You can also get FREE CCNA and CCNP exam questions every day! And coming in 2007 — Microsoft Vista certification from The Bryant Advantage!

Learn About CCNP Certification Cisco CCNA Certification RHCE Certification

Passing Cisco’s CCNA and CCNP Exams: Traceroute

Writen by Chris Bryant

In preparation for your CCNA and CCNP exam success, you’ve got to learn to troubleshoot Cisco routers. And while ping is a great basic IP connectivity tool, it doesn’t give you all the information you need to diagnose network connectivity issues.

Let’s say you have six routers between CityA and CityB. You send a ping from A to B, and get this return:

R1#ping 172.1.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.1.1.1, timeout is 2 seconds:

…..

Success rate is 0 percent (0/5)

The five periods indicate that there is no IP connectivity to CityB. Problem is, that’s about all ping tells you. You can have 5 or 50 routers between the two points, so how can you tell which downstream router has the problem?

That’s where traceroute comes in. Traceroute sends three datagrams with a Time To Live (TTL) of 1. Those datagrams will timeout once they hit the first router in the path, and that router will respond with an ICMP Time Exceeded message.

In response, the sending router sends three more datagrams, but these have a TTL of 2. This means that the next router in line will send back ICMP Time Exceeded messages. This process continues until the final destination (CItyB) is reached the output of the command shows us the path the data took:

Router1#traceroute 271.1.1.1

Type escape sequence to abort.

Tracing the route to 271.1.1.1

1 20.1.1.1 4 msec 4 msec 4 msec

2 30.1.1.1 20 msec 16 msec 16 msec

3 271.1.1.1 16 msec * 16 msec

How does this help troubleshoot a problem? Let’s say that the second router in this path, 30.1.1.1, doesn’t know how to get to 271.1.1.1. The output would look like this:

Router1#traceroute 271.1.1.1

Type escape sequence to abort.

Tracing the route to 271.1.1.1

1 20.1.1.1 4 msec 4 msec 4 msec

2 30.1.1.1 20 msec 16 msec 16 msec

3 * * *

This indicates that the router at 30.1.1.1 doesn’t know how to get to the final destination. Now you have a better idea of which router has an issue!

Now here’s the bad part: you’re going to get 30 lines of three asterisks, and until you abort this traceroute, you’re going to just watch those asterisks go across the screen. There’s an abort sequence that the router mentions in the first line of the console output, but the router doesn’t tell you what it is! So I will - this top-secret sequence is TWICE, one right after the other.

That keystroke takes a little getting used to, but a CCNA or CCNP can do it! Add this command to your Cisco skill set, and it will serve you well both on the CCNA and CCNP exams and your real-world networks. And you’ll impress your friends by knowing how to stop a traceroute!

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of free CCNA and CCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.
For a FREE copy of his latest e-books, “How To Pass The CCNA” and “How To Pass The CCNP”, visit the website and download your free copies. You can also get FREE CCNA and CCNP exam questions every day! Pass the CCNA exam with The Bryant Advantage!

Learn About CCNP Certification Cisco CCNA Certification RHCE Certification

Four Important Commands For Your CCNA / CCNP Home Lab

Writen by Chris Bryant

More CCNA and CCNP candidates than ever before are putting together their own home practice labs. It’s more affordable than it ever has been, and I receive emails daily from new CCNAs and CCNPs who say it’s the best thing they could have done to improve their studies.

There are some commands you can configure on your lab routers that won’t necessarily be on your CCNA or CCNP exams, but they will make life a lot easier for you. Let’s take a look at just a few of these.

The command “no exec” is short, yet powerful. Occasionally you’ll have what is referred to as a “rogue EXEC” process tie up a line, and you end up having to continually clear lines, which disrupts your practice. If you have an access server, I highly recommend you configure this command on your lines, as shown here:

ACCESS_SERVER(con)#line 1 8

ACCESS_SERVER(con)#no exec

From your CCNA studies, you know that the command “no ip domain-lookup” prevents a Cisco router from sending a broadcast to find a DNS server anytime you enter something that is not an IOS command - and that includes mistyped commands, which happens to all of us sooner or later. Make sure to run that command in global configuration mode on all your practice routers.

There are two commands I like to configure on the console line on all my practice routers and switches. The first is “exec-timeout 0 0″, which prevents you from being kicked out of enable mode and back into user exec after a few minutes of inactivity. (This doesn’t sound like much, but you’ll get pretty tired of typing “enable” after a while.) The first zero refers to minutes, the second zero to seconds. Setting them both to zero disables the exec-timeout function.

The second command prevents the router from interrupting the command you’re typing with a console message. If you’ve ever been in the middle of typing a router command and suddenly you’re interrupted with a logging message, you know that can be pretty annoying. We don’t want the router to not display the message, but we do want the router to wait until we’re done entering data. The command to perform this is “logging synchronous”.

R1(config)#line console 0

R1(config-line)#exec-timeout 0 0

R1(config-line)#logging synchronous

You won’t see many of these commands on your exams, but after you configure them on your home lab devices, you’ll wonder how you did without them!

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of free CCNA and CCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.
For a FREE copy of his latest e-books, “How To Pass The CCNA” and “How To Pass The CCNP”, visit the website and download your free copies. You can also get FREE CCNA and CCNP exam questions every day! Pass the CCNA exam with The Bryant Advantage!

Learn About CCNP Certification Cisco CCNA Certification RHCE Certification