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.)
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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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As your CCNA / CCNP home lab expands, an access server such as the Cisco 2509 or 2511 is one of the best investments you can make. In this article, we’ll look at the basic configuration for an access server and discuss how to connect to the other routers and switches in your pod through the AS.

Here’s part of a configuration from one of my access servers:

ip host FRS 2006 100.1.1.1

ip host SW2 2005 100.1.1.1

ip host SW1 2004 100.1.1.1

ip host R2 2002 100.1.1.1

ip host R1 2001 100.1.1.1

ip host R3 2003 100.1.1.1

interface Loopback0

ip address 100.1.1.1 255.255.255.255

no ip directed-broadcast

This is an IP Host table, and this is what makes the entire AS setup work. Your PC will connect to the access server, and the access server is in turn physically connected to your other routers and switches via an octal cable. One end of the octal cable splices off into eight separate cables, each terminated with an Rj-45 connector. That connector will be placed into the console port of one of your home lab devices. In this configuration, I have connector 1 connected to the console port of R1, connector 2 to R2, connector 3 to R3, connector 4 to Sw1, and so forth. (The connectors are physically numbered as well.)

The IP Host table entries here are linked to the loopback address shown. The loopback can be any address, but it must match the address in the IP Host table. This allows you to create reverse telnet sessions to the routers and switches.

To open the reverse telnet sessions upon opening a connection to the AS, type the entire name of the device and press the enter key twice. A connection to that device will now be visible, as shown here:

Access_Server#r1

Trying R1 (100.1.1.1, 2001)… Open

R1#

To get back to the access server, use the key combination followed by pressing the “x” key. Keep doing this until you’ve opened a connection to every router and switch in your pod.

Once you’ve opened the lines, you will not use the full device name to connect to the home lab devices. You should press only the number corresponding to the reverse telnet session you opened. For instance, in this configuration I opened telnet session 1 to R1, session 2 to R2, and session 3 to R3. Once I opened those sessions, I just use those numbers to reconnect to the devices, as shown here:

Access_server#1

[Resuming connection 1 to r1 ... ]

R1#

Access_server#2

[Resuming connection 2 to r2 ... ]

R2#

Access_server#3

[Resuming connection 3 to r3 ... ]

R3#

If you type the full hostname again after initially opening the connection, you will see this message:

Access_server#r1

Trying R1 (100.1.1.1, 2001)…

% Connection refused by remote host

The connection is refused because you already have an open connection to that router.

There’s one more important part of an access server config your CCNA / CCNP home lab will need:

line 1 8

no exec

transport input all

The line numbers may differ according to your access server, but “no exec” is very important here. This will stop rogue EXEC sessions from refusing connections that it shouldn’t be refusing. Without this command, you’ll commonly see “connection refused by remote host” when you shouldn’t be. That message is the most common error you’ll see on an access server, and it’s there because you already have an open connection or you left “no exec” out of your configuration. “No exec” isn’t mandatory, but it will help you keep your sanity!

A Cisco home lab is an invaluable study tool when you’re preparing for CCNA and CCNP exam success. Once you’ve gotten a couple of routers and switches, you’ll quickly get tired of moving that blue console cable every time you want to configure a different device. The solution to this problem is purchasing and configuring an access server (AS).

For those of you new to access servers, note that these are not white boxes running Microsoft operating systems. These are Cisco routers that allow you to connect to all the routers and switches in your home lab without moving a cable. You can physically or logically connect to the access server and work with all your devices from there.

When you’re pricing access servers, please remember that you do NOT need an expensive AS. Right now on ebay there are access servers costing up to $5000 – this is NOT what you want to buy. What you’re looking for is something like a 2509 or 2511, which is going to run you anywhere from $100 – $200. It’s money well spent, because once you get an AS, you’ll really wonder how you ever did without it.

The only additional hardware you need is the cable that will physically connect your AS to the other routers and switches in your home lab. The cable you need is called an octal cable, so named because one end of this cable is actually eight ends, all terminated with a numbered RJ-45 connector.

The large end of the cable is going to be connected to the AS itself. The cable will connect to a port on the AS that will have “async 1-8″ directly above the physical port. It is this port that makes an AS different from other Cisco routers.

Once you’ve got your AS and this cable, you’re ready to configure your AS. Connect the cable to the AS as described above, and then you will connect one of the RJ-45 connectors to the console port of each one of your routers and switches. Make sure to note the number that’s on the cable itself right below the connector, because that’s very important. In the next part of this home lab tutorial, I’ll tell you exactly how to configure your access server for best results, along with a few troubleshooting tips.

Occasionally, during your CCNA and CCNP studies, you’ll run into a term that just doesn’t quite make sense to you. (Okay, more than occasionally!) One such term is “reverse telnet”. As a Cisco certification candidate, you know that telnet is simply a protocol that allows you to remotely connect to a networking device such as a router or switch. But what is “reverse telnet”, and why is it so important to a Cisco CCNA / CCNP home lab setup?

Where a telnet session is started by a remote user who wants to remotely control a router or switch, a reverse telnet session is started when the host device itself imitates the telnet session.

In a CCNA / CCNP home lab, reverse telnet is configured and used on the access server. The access server isn’t a white box server like most of us are used to; an access server is a Cisco router that allows you to connect to multiple routers and switches with one session without having to move a rollover cable from device to device.

Your access server will use an octal cable to connect to the other routers and switches in your home lab. The octal cable has one large serial connector that will connect to the access server, and eight rj-45 connectors that will connect to your other home lab devices. Your access server then needs an IP Host table in order to perform reverse telnet.

An IP Host table is easy to put together (and you better know how to write one to pass the CCNA!). The IP Host table is used for local name resolution, taking the place of a DNS server. A typical access server IP Host table looks like this:

ip host FRS 2007 100.1.1.1

ip host R3 2003 100.1.1.1

ip host R1 2001 100.1.1.1

ip host R2 2002 100.1.1.1

ip host R4 2004 100.1.1.1

ip host R5 2005 100.1.1.1

ip host SW1 2006 100.1.1.1

interface Loopback0

ip address 100.1.1.1 255.255.255.255

no ip directed-broadcast

This configuration will allow you to use your access server to connect to five routers, a frame relay switch, and a switch without ever moving a cable. When you type “R1″ at the console line, for example, you’ll be connected to R1 via reverse telnet. If you have a smaller lab, an access server is still a real timesaver and an excellent investment. And by getting a static IP address to put on your access server, you can even connect to your home lab from remote locations!