One of the most common questions I get from CCNA and CCNP candidates who are setting up their own home labs is “What cables will I need?” The answer is “It depends.” As you know from your exam studies, the physical layout of your lab is what determines the cables you’ll need. Let’s take a look at the most common home lab cable types and when you will need them.

Straight-through cables have quite a few uses in a CCNA / CCNP home lab. You’ll need them to connect a switch port to an AUI port on a router (and you’ll need a transceiver for that as well). If you have an ISDN simulator, straight-through cables can be used to connect a router’s BRI port to the simulator.

Crossover cables are used to connect switches and allow them to trunk. If at all possible, get two switches in your home lab. This will allow you to gain valuable experience in manipulating root bridge election, working with STP, and creating EtherChannels.

DTE/DCE cables are used to connect two routers via their serial cables. If you are planning on using a frame relay switch in your lab, you’ll need several of these. You can also get some great practice in by directly connecting two routers and bringing the connection up (and making sure it stays up!). This is valuable practice for your CCNA exam.
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A prime topic of your CCNA and CCNP CIT exams will be connecting Cisco routers directly via their Serial interfaces, and while the configuration is straightforward, there are some vital details and show commands you must know in order to pass the exams and configure this successfully in production and home lab networks. Let’s take a look at a sample configuration.

Connecting Cisco routers directly via their Serial interfaces works really well once you get it running – and getting such a connection up and running is easy enough. You can use show controller serial x to find out which endpoint is acting as the DCE, and it’s the DCE that must be configured with the clockrate command.

R3#show controller serial 1

HD unit 1, idb = 0×11B4DC, driver structure at 0×121868

buffer size 1524 HD unit 1, V.35 DCE cable

R3(config)#int serial1

R3(config-if)#ip address 172.12.13.3 255.255.255.0

R3(config-if)#clockrate 56000

R3(config-if)#no shut

Failure to configure the clockrate has some interesting effects regarding the physical and logical state of the interfaces. Let’s remove the clockrate from R3 and see what happens.

R3(config)#int s1

R3(config-if)#no clockrate 56000

R3(config-if)#

18:02:19: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to down

The line protocol doesn’t drop immediately, but it does drop. Let’s run show interface serial1 to compare the physical and logical interface states.

R3#show int serial1

Serial1 is up, line protocol is down

Physically, the interface is fine, so the physical interface is up. It’s only the logical part of the interface – the line protocol – that is down. It’s the same situation on R1.

R1#show inter serial1

Serial1 is up, line protocol is down

While a router misconfiguration is the most likely cause of a serial connection issue, that’s not the only reason for clocking issues. Cisco’s website documentation mentions CSU/DSU misconfiguration, out-of-spec cables, bad patch panel connections, and connecting too many cables together as other reasons for clocking problems. Still, the number one reason for clocking problems in my experience is simply forgetting to configure the clockrate command!

More CCNA and CCNP candidates than ever before are putting together their own home labs, and there’s no better way to learn about Cisco technologies than working with the real thing. Getting the routers and switches is just part of putting together a great CCNA / CCNP home lab, though. You’ve got to get the right cables to connect the devices, and this is an important part of your education as well. After all, without the right cables, client networks are going to have a hard time working!

For your Cisco home lab, one important cable is the DTE/DCE cable. These cables have two major uses in a home lab. To practice directly connecting Cisco routers via Serial interfaces (an important CCNA skill), you’ll need to connect them with a DTE/DCE cable. Second, if you plan on having a Cisco router act as a frame relay switch in your lab, you’ll need multiple DTE/DCE cables to do so. (Visit my website’s Home Lab Help section for a sample Frame Relay switch configuration.)

If you have multiple switches in your lab, that’s great, because you’ll be able to get a lot of spanning tree protocol (STP) work in as well as creating Etherchannels. To connect your switches, you’ll need crossover cables.

You’ll need some straight-through cables as well to connect your routers to the switches.

Finally, if you’re lucky enough to have an access server as part of your lab, you’ll need an octal cable to connect your AS to the other routers and switches in your lab. The octal cable has one large connector on one end and eight numbered RJ-45 connectors on the other end. The large connector should be attached to the async port on your AS, and the numbered RJ-45 connectors will be connected to the console ports on your other routers and switches.

Choosing and connecting the right cables for your Cisco CCNA / CCNP home lab is a great learning experience, and it’s also an important part of your Cisco education. After all, all great networks and home labs all begin at Layer One of the OSI model!