To pass the CCNA exam and earn that coveted certification, you’ve got to know Cisco switches inside and out. Among the many important details you’ve got to know are the three methods that Cisco switches use to forward frames, and the differences between the three.

The first switching method is Store-and-Forward. The name is the recipe, because that’s just what the switch does – it stores the entire frame before beginning to forward it. This method allows for the greatest amount of error checking, since the Frame Check Sequence (FCS) can be run before the frame is forwarded. As always, there is a tradeoff, since this error checking process makes this the slowest of the three frame forwarding methods.

The quickest method is Cut-Through, where only the destination MAC address of the frame is examined before the forwarding process begins. This means that the part of the frame is actually being forwarded as it is still being received! The tradeoff here is that the FCS does not run, so there is absolutely no error checking with Cut-Through switching.
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CCNA / CCNP candidates are going to be drilled by Cisco when it comes to troubleshooting questions. You’re going to have to be able to analyze configurations to see what the problem is (and if there is a problem in the first place), determine the meaning of different debug outputs, and show the ability not just to configure a router or switch, but troubleshoot one.

That’s just as it should be, because CCNAs and CCNPs will find themselves doing a lot of troubleshooting in their careers. Troubleshooting isn’t something that can just be learned from a book; you’ve got to have some experience working with routers and switches. The only real way to learn how to troubleshoot is to develop that ability while working on live equipment.
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To be truly prepared for your CCNA and CCNP exams, you need real hands-on experience with real Cisco routers and switches. However, a production network is a really bad place to practice your configurations, but an excellent way to get fired and/or sued. The key to becoming a true CCNA and CCNP is assembling your own Cisco home lab.

You don’t have to spend a lot of money to do so; used Cisco equipment is cheaper than ever. It’s robust as well – I’ve bought literally hundreds of used routers and switches over the years and have had very few problems. I owe much of my skill to practicing configurations and troubleshooting in my own home lab.
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I know from experience that part of the excitement and anxiety of putting together your own CCNA / CCNP home lab is deciding what to buy! While you can make a workable home lab out of almost any combination of Cisco routers and switches, some routers are better suited for home lab work than others because they can fill multiple roles.

My personal favorite is the Cisco 2520. This router has four serial interfaces, making it an ideal frame relay switch. Don’t forget that just because you’re using a router as a frame switch, you can still use its routing capabilities. One setup I use is to use three of the four serial interfaces for frame switching and the fourth interface as a point-to-point network with another router. All you need is some DTE/DCE cables and you’re all set.
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I know from experience that part of the excitement and anxiety of putting together your own CCNA / CCNP home lab is deciding what to buy! While you can make a workable home lab out of almost any combination of Cisco routers and switches, some routers are better suited for home lab work than others because they can fill multiple roles.

When you buy CCNA or CCNP “lab kits” – bundles of routers and switches – you can get a little confused about whether you’re getting a good deal. One router I get asked about quite a bit is the 2503.

2503 routers are fantastic for CCNA and CCNP home labs. They come with two serial interfaces, allowing you to connect one interface directly to another router (you’ll need a DTE/DCE cable for that, too) while connecting another to a frame relay switch if you like. If you don’t have a frame relay switch, you can connect a 2503 directly to two other routers via the serial interfaces.
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A Cisco access server is generally the last item a CCNA or CCNP candidate has on their mind when they’re putting together a home lab. The thinking tends to be that since this router isn’t really doing anything in the production part of your practice lab, it’s not really important.

Once you have more than two devices in your home lab, though, you’ll realize that constantly moving the console cable around from one router to another gets very tiresome. That’s what an access server does for a home lab – it allows you to connect your PC to a single device when working in your home lab, with no need to constantly disconnect and reconnect the console cable. The console cable will be connected directly to the access server, and the access server is connected to all the other devices in your home lab. Once you start working with one, you’ll wonder how you got along without it!

The term “access server” is a little misleading. This is not a server in the traditional sense, it’s a Cisco router with asynchronous serial ports. It is these ports that you’ll use to connect to the other devices in your home lab. Two affordable models of access servers are Cisco 2509s and Cisco 2511s. They can be found on ebay as well as other vendors on the Net.

You will also need an octal cable. On one end, the cable has a large connector that will connect to the access server. The other end is actually eight separate cables, each with RJ-45 connectors. These connectors are numbered 1 – 8 and will be connected to the console port on each router and switch. It is important to note the number on each connector you’re connecting to the other lab devices.

Now that you’ve got the physical equipment, let’s take a look at a typical configuration of an access server:

no service password-encryption

no service udp-small-servers

no service tcp-small-servers

! hostname BRYANT_ADVANTAGE_AS4

no ip domain-lookup

ip host r1 2001 10.4.4.4

ip host r2 2002 10.4.4.4

ip host r3 2003 10.4.4.4

ip host sw1 2004 10.4.4.4

ip host sw2 2005 10.4.4.4

ip host FrameSwitch 2006 10.4.4.4

interface Loopback555

ip address 10.4.4.4 255.255.255.0

line con 0

exec-timeout 0 0

logging synchronous\

line 1 16

no exec

transport input all

You can assign any loopback address and number here the important thing to note is that the IP HOST table you will build constantly refers back to the loopback address on the access server.

In this configuration, I have the octal cable’s connector 1 in R1, 2 in R2, 3 in R3, 4 in SW1, 5 in SW2, and 6 in my frame relay switch. The number “2001″ in the first line of the IP HOST table refers to that connector. That’s why it is important to note the number on a given connector you place in the console port of a router or switch.

The asynchonous lines are identified by “line 1 16″. This access server has 16 possible connections many will just have 8, which is usually plenty. Regardless of how many lines you have, you’ll need the commands transport input all and no exec to allow reverse telnet to work effectively.

There’s one more thing to watch out for. When you first connect to the AS for a practice session, you will need to open the line to each device by using the full hostname of the device as shown in the IP HOST table. Here, you would begin by entering R1, R2, R3, SW1, SW2, and FrameSwitch to open the line to each device. After that, you need to enter the line number – 1, 2, 3, 4, 5, and 6. It sounds a little confusing at first, but after just a few minutes of practice you’ll be doing it without even thinking about it.

When you are working in your home lab, you will not go from one device to another that is, when you are done on R1 and want to configure R2, you must go back to the access server and then to R2. The keystroke to do this is . Again, it may sound complicated, but after a little practice you will again do this without thinking about it.

Adding an access server to your CCNA or CCNP home lab may not be on your mind now, but once you add a few more routers or switches to the lab, you’ll want to spend more time configuring and practicing and less time moving a cable around. And once you get one, you’ll wonder how you did without it!