Cisco CCNA / CCNP Tutorial: Home Lab Assembly Case Study

Part of your CCNA / CCNP education is deciding what network topology to use when you’re putting together your home lab. Some of you are starting with one or two routers or switches, while others are starting with more. A customer recently sent me a list of his Cisco routers and switches that he has available for a home lab and asked for my help in coming up with the best way to use them.

There is no “right” or “wrong” answer to this question; again, part of the learning process is configuring and reconfiguring the physical topology of your lab. Let’s look at the routers and switches he has available, including the interfaces on each, and come up with one possible CCNA / CCNP home lab setup.

The equipment list:

Two 3620 routers. Each has 1 serial port and 2 ethernet ports.

One 3640 router. This has two ethernet cards, each with two ports, and two AUI ports.

Three 2503s, my personal favorite for home labs! These have 1 AUI port, 2 serial interfaces, and one BRI interface apiece.

One 2524 router. This has one serial port, 1 ethernet port, and one BRI interface.

One 4500 router. This has eight BRI ports, 2 ethernet ports, and more importantly, four serial ports.

He also has a 5200 access server, an ISDN simulator, one 2924 switch, and one 1924 switch.

Now, if you don’t have this much equipment to work with, don’t panic! Most CCNA / CCNP candidates don’t; this is more of an exercise in looking at what you do have and using it to the utmost.

As I’ve mentioned in many of my CCNA / CCNP home lab articles, an access server is a great thing to have. All he needs is an octal cable to connect his AS to the other devices we choose to use, and he’s all set. (If you need an access server sample configuration, there is one on my website in the Home Lab section.)

A frame relay switch is also great to have, and the 4500 will make a great FR switch. Having a frame relay cloud in your CCNA / CCNP home lab is a great way to get experience configuring and troubleshooting frame relay, an essential skill for CCNA success.

I would put both of the 3620s on the frame relay cloud via the Serial interface, as well as two of the 2503s. That gives you four routers that will be using frame relay to communicate, and that’s the most we can have since the 4500 has four serial ports. The 4500 will need to be configured as a frame relay switch and connected to the other routers via a DTE/DCE cable. (Again, if you need a frame relay switch configuration, the one I use in my pods is on the website in the same place as the access server configuration.)

The two 2503s that are on the frame relay cloud should also be connected via their BRI interfaces. The home lab also includes an ISDN simulator, which is necessary to allow routers to communicate via their BRI interfaces. Just get a couple of straight-through cables to connect those two routers to the ISDN simulator and that segment is ready to go. (Remember that you can’t connect Cisco routers directly via their BRI interfaces.)

All of the routers in this lab have at least one ethernet or AUI port, so we can connect them all to either one of the switches. The switches should be connected via at least two crossover cables to allow practice with trunking, root bridge election, and VLANs. Having two switches really does add quite a bit to a CCNA / CCNP home lab’s capabilities. You can experiment with different subnets and vlans with as well. Don’t be afraid to dive in – that’s what a home lab is all about!

So now we’ve got four routers connected via frame relay, two via ISDN, and the others via ethernet segments. Two of the routers that are not using their serial interfaces should be connected directly via their serial ports. For this, you’ll just need another DTE/DCE cable. Knowing how to bring up the line between two directly connected serial ports is an important CCNA skill, and so is troubleshooting it. You should be able to bring such a connection up with your eyes closed, and once you work with your own CCNA / CCNP home lab, you’ll be able to!

Also, don’t forget to add a loopback interface to each one of your routers. I like to use 1.1.1.1 for R1, 2.2.2.2 for R2, and so on. Advertising loopbacks is another great way to get practice with RIP, OSPF, EIGRP, IGRP, and static routing.

We’ve taken a pile of routers and switches and turned them into a fantastic CCNA / CCNP home lab. Whether you’re working with two Cisco devices or ten, coming up with your own home lab topology is a great learning experience and the beginning of developing your analytical and troubleshooting skills.

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Cisco CCNP / BCMSN Exam Tutorial: Changing Root Bridge Election Results

Your BCMSN and CCNP studies will include mastering the details of Spanning Tree Protocol (STP). While you learned some of these details in your CCNA studies, quite a bit of it may be new to you. Before going on to the intermediate and advanced STP features, let’s review the root bridge election process and learn how to change these results.

Each switch will have a Bridge ID Priority value, more commonly referred to as a BID. This BID is a combination of a default priority value and the switch’s MAC address, with the priority value listed first. For example, if a Cisco switch has the default priority value of 32,768 and a MAC address of 11-22-33-44-55-66, the BID would be 32768:11-22-33-44-55-66. Therefore, if the switch priority is left at the default, the MAC address is the deciding factor.

Switches are a lot like people – when they first arrive, they announce that they are the center of the universe! Unlike some people, the switches will soon get over it. BPDUs will be exchanged until one switch is elected Root Bridge, and it’s the switch with the lowest BPDU that will end up being the Root Bridge.

If STP is left totally alone, a single switch is going to be the root bridge for every single VLAN in your network. Worse, that single switch is going to be selected because it has a lower MAC address than every other switch, which isn’t exactly the criteria you want to use to select a single root bridge.

The time will definitely come when you want to determine a particular switch to be the root bridge for your VLANs, or when you will want to spread the root bridge workload. For instance, if you have 50 VLANs and five switches, you may want each switch to act as the root bridge for 10 VLANs each. You can make this happen with the spanning-tree vlan root command.

SW1(config)#spanning-tree vlan 1 ?

forward-time Set the forward delay for the spanning tree

hello-time Set the hello interval for the spanning tree

max-age Set the max age interval for the spanning tree

priority Set the bridge priority for the spanning tree

root Configure switch as root

In this example, we’ve got two switches, and SW1 has been elected the root bridge for VLANs 10, 20, and 30. We’ll use the spanning-tree vlan root command on SW2 to make it the root bridge for VLANs 20 and 30.

SW2(config)#spanning-tree vlan 20 root primary

SW2(config)#spanning-tree vlan 30 root primary

SW2#show spanning vlan 20

VLAN0020

Spanning tree enabled protocol ieee

Root ID Priority 24596

Address 000f.90e2.1300

This bridge is the root

SW2#show spanning vlan 30

VLAN0030

Spanning tree enabled protocol ieee

Root ID Priority 24606

Address 000f.90e2.1300

This bridge is the root

SW 2 is now the root bridge for both VLAN 20 and 30. Notice that the priority value has changed from the default of 32768.

In the next CCNP / BCMSN tutorial, we’ll take a look at more STP features.

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Cisco CCNA Certification: The Importance Of The OSI Model

There’s nothing I enjoy more than teaching Cisco technologies, especially CCNA candidates. Whether it’s in-person or online, everyone’s excited to be there. There’s a sense of anticipation in the air, and everyone is ready to work hard, get their hands on the racks of Cisco routers and switches I
have available…

… and then I break out the OSI model chart. Chins slump. People sigh, or at least wish they hadn’t ordered decaf that morning.

Okay, it’s not that bad. But it does temper the excitement a little. I always get a sense of “why can’t we just hurry up and get on the routers and switches? Why do we have to learn this dry stuff?”

One reason is that Cisco demands you know the OSI model inside and out for both the Intro and ICND exams. You have to admit that’s a pretty good reason, but still, students find the OSI model information to be very dry.

I understand that, because I’ve been there. My first exposure to the OSI model was actually in a Novell “Networking Technologies” class, and man, was that chart ever dry. They crammed every known protocol (and some unknown ones, I think) into the OSI model. It looked like a giant jigsaw puzzle, and the real problem is that I didn’t know what the heck most of that stuff was.

So I dutifully attempted to memorize this massive chart. I managed to pass the exam, but I wondered what all that effort had really been for. It’s not like you sit around in a server room or wiring closet and discuss the OSI model.

As a CCNA candidate, you don’t have to worry about all the protocols I memorized way back when, but you do have to know what happens at each layer. Which leads to this question:

“If I work with routers and switches, why do I have to know about all the other layers? Don’t routers and switches just work at layer 2 and 3?”

Yes, switches work at Layer 2 and routers at Layer 3. But to truly understand networking, you’ve got to understand what happens at the other layers. Why?

Most network administrators and engineers are going to spend a lot more time troubleshooting than installing. That’s just the way it is. And to troubleshoot effectively, you’ve got to know what’s going on at all layers of the OSI model, not just layers 2 and 3.

As someone who’s done a lot of hiring and conducted a great many job interviews, I can tell you that the ability to troubleshoot is the number one quality I look for. That’s why I tell CCNA and CCNP candidates that they’ve got to get all the hands-on practice they can while I understand the importance of theory, the only way to develop troubleshooting ability is to work on the real deal. No simulator program
is going to teach you how to troubleshoot.

Additionally, the only way to truly develop your troubleshooting abilities is to know what’s going on over the entire network, not just the routers and switches. Troubleshooting always starts at Layer 1 if you don’t find a problem at the Physical layer, and everything’s fine with your routers and switches, how are you going to continue troubleshooting if you don’t know what the next steps are as data moves closer to the end user?

So when it comes to the OSI model, don’t just give it a quick once-over and move on to the fun stuff in your CCNA studies. The tangible benefit of passing your exams is great, but it’s the hidden benefit of developing your own troubleshooting methodology that makes mastering the OSI model worthwhile.

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