Four Important Commands For Your CCNA / CCNP Home Lab

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!

Cisco Certification: The "Secret" Key To Getting Your CCNA And CCNP

Whether you're working on your CCNA or CCNP, Cisco certification exams are the most demanding computer certification exams in the IT field. Cisco exams are not a test of memorization, they're a test of your analytical skills. You'll need to look at configurations and console output and analyze them to identify problems and answer detailed questions. To pass these demanding exams, you've got to truly understand how Cisco routers and switches operate - and the key to doing so is right in front of you.

The debug command.

Of course, there is no single "debug" command. Using IOS Help, you can quickly see that there are hundreds of these debugs, and I want to mention immediately that you should never practice these commands on a production router. This is one major reason you need to get some hands-on experience with Cisco products in a home lab or rack rental. No software program or "simulator" is going to give you the debug practice you need.

Now, why am I so insistent that you use debugs? Because that's how you actually see what's going on. It's not enough to type a frame relay LMI command, you have to be able to see the LMIs being exchanged with "debug frame lmi". You don't want to just type a few network numbers in after enabling RIP, you want to see the routes being advertised along with their metrics with "debug ip rip". The list goes on and on.

By using debugs as part of your CCNA and CCNP studies, you're going beyond just memorizing commands and thinking you understand everything that's happening when you enter a command or two. You move to a higher level of understanding how routers, switches, and protocols work -- and that is the true goal of earning your CCNA and CCNP.

Cisco CCNA Certification Exam Tutorial: Variance And Unequal Cost Load Balancing

To pass the CCNA exam, you've got to know how to work with IGRP and EIGRP unequal-cost load balancing. You may not see much IGRP in production networks anymore, but you'll see a lot of EIGRP, and part of fine-tuning your EIGRP network is making sure that all paths are in use while allowing for varying bandwidth rates.

Using the variance command is the easy part - it's getting the metric that's the hard part with IGRP. With EIGRP, you just look in the topology table and that's it. With IGRP, you've got to run a debug to get the right metric.

The variance command is a multiplier when the value supplied with the variance command is multiplied by the lowest-cost metric, it must exceed the higher-cost metric in order for the higher-cost route to be added.

If that sounds complicated, it's not. It's one of those things that sounds difficult, but isn't. Trust me!

In this example, R1 has two paths to 172.23.0.0, but is currently using only one. By looking in the IP routing table, we've seen that the lowest-cost metric for network 172.23.0.0 on R1 is 8576. This path goes through the 172.12.123.0 network. There is another valid path that uses the 172.12.13.0 network, but is not currently in use.

I 172.23.0.0/16 [100/8576] via 172.12.123.2, 00:00:53, Serial0

IGRP does not have a “show" command that displays all valid routes to a destination, as does EIGRP. The command debug ip igrp transactions will show the current metric of the routes using the 512 KBPS route.

R1#debug ip igrp transactions

IGRP protocol debugging is on

19:17:51: IGRP: broadcasting request on Loopback0

19:17:51: IGRP: broadcasting request on Serial0

19:17:51: IGRP: broadcasting request on Serial1

19:17:51: IGRP: received update from 172.12.13.3 on Serial1

19:17:51: subnet 172.12.13.0, metric 23531 (neighbor 21531)

19:17:51: subnet 172.12.123.0, metric 23531 (neighbor 8476)

19:17:51: network 1.0.0.0, metric 24031 (neighbor 8976)

19:17:51: network 2.0.0.0, metric 22131 (neighbor 1600)

19:17:51: network 3.0.0.0, metric 22031 (neighbor 501)

19:17:51: network 172.23.0.0, metric 21631 (neighbor 1100)

R1(config)#router igrp 1
R1(config-router)#variance 3
R1#show ip route 172.23.0.0
Routing entry for 172.23.0.0/16
Known via "igrp 1", distance 100, metric 8576
Redistributing via igrp 1
Advertised by igrp 1 (self originated)
Last update from 172.12.123.2 on Serial0, 00:00:01 ago
Routing Descriptor Blocks:
* 172.12.13.3, from 172.12.13.3, 00:00:20 ago, via Serial1
Route metric is 21631, traffic share count is 1
Total delay is 21000 microseconds, minimum bandwidth is 512 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 0
172.12.123.3, from 172.12.123.3, 00:00:20 ago, via Serial0
Route metric is 8576, traffic share count is 3
Total delay is 21000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 0
172.12.123.2, from 172.12.123.2, 00:00:01 ago, via Serial0
Route metric is 8576, traffic share count is 3
Total delay is 21000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 0

The metric for 172.23.0.0 through the direct connection is 21631. A variance of 3 means that any route with a metric less than the best metric multiplied by the variance (in this case, 8576 x 3 = 25728) will be entered into the routing table. R1 now has three unequal-cost paths to 172.23.0.0 in its routing table, and load balancing will take place.

IGRP unequal-cost load balancing takes some practice, but as you can see, once you get the metric it's easy to work with. Just make sure you know how to get that metric!

Cisco CCNA Certification Exam: Five Frame Relay Details You Must Know

When you're studying for your CCNA exam on the way to earning this coveted Cisco certification, the details can seem overwhelming! In this article, I'll point out five Frame Relay details that you must keep in mind when you're on your way to the CCNA exam!

Inverse ARP starts working as soon as you open the serial interface. This protocol performs dynamic Frame Relay mapping, but you don't have to enable it - it's already enabled as soon as you enter the command "encapsulation frame-relay".

When you're configuring Frame Relay map statements manually, remember that you're mapping the local DLCI to the remote IP address.

When you run "show frame map", the word "dynamic" indicates mappings created by Inverse ARP, and "static" indicates it was manually created.

To spot possible LMI type mismatches, run "show frame lmi". A large number of Status Timeouts indicates that there may be an LMI problem between your router and the frame relay switch.

This last one is for the many of you building CCNA home labs. A frame relay switch is a great addition to your lab! While you're busy putting the configuration together, don't forget the global command "frame-relay switching" - it's this command that allows a Cisco router to act as a frame relay switch!

Cisco CCNA / CCNP Exam Tutorial: Five Debugs You Must Know

To pass the BSCI exam and move one step closer to CCNP certification success, you've got to know how and when to use debug commands to troubleshoot and verify network operations. While you should never practice debug commands on a production network, it's important to get some hands-on experience with them and not rely on "router simulators" and books to learn about them.

When it comes to RIP, "debug ip rip" is the primary debug to use. This debug will show you the contents of the routing update packets, and is vital in diagnosing RIP version mismatches and routing update authentication issues.

You know how to use the variance command to configure unequal-cost load-sharing with IGRP, but IGRP has no topology table that will give you the feasible successor metrics you need. With IGRP, you need to use the "debug ip igrp transactions" command to get these vital metrics.

Several factors are considered by OSPF-enabled routers when it comes to forming adjacencies, including hello and dead timer settings. If an adjacency doesn't form when you think it should, run "debug ip ospf adj". The reason the adjacency isn't forming is usually seen quickly with this command's output.

Let's not ignore Layer Two! If frame relay mappings are not forming according to your configuration, run "debug frame lmi". This debug will allow you to quickly diagnose and correct any LMI mismatches.

When it comes to PPP, it can be very frustrating to try to spot a problem with a password or username. Instead of staring at the configuration for 10 minutes, run "debug ppp negotiation" and send a ping over the link. This command will help you spot the router with the misconfigured username or password, not to mention saving you a lot of time!


Effectively using debugs during your CCNA and CCNP exam study will help you truly understand what's going on "behind the command" - and it will really come in handy on that day when your production network just isn't doing what you (think) you told it to do!