Straight Talk on Network Cables

By Ronald Pacchiano | Posted November 12, 2004

I have my own real estate business with a few employees, and I typically maintain our company's computers and network equipment myself. Now I might not be the best IT person, but for the most part I've been able to handle the majority of our network problems.

The other day while setting up some network equipment in a new location, I ran into a rather annoying problem. I was attempting to connect two switches together but forgot to pick up a crossover cable. I had a collection of cables in a box collecting dust, but they were all the same color and none of them were labeled, so I had no idea which ones were crossover cables and which were straight-through cables. It took forever for me to test each of those cables before finally stumbling upon the crossover cable I needed.

I know there's a way to identify a crossover cable from a straight-through cable just by looking at it, but I don't know how. Also, I don't understand in what situation I should use a crossover cable over a straight-through one. Does one perform better then the other or is one simply an updated version of the other? Could you shed some light on this? Please tell me how I can identify the difference between these cables and point out some situations where I should use one over the other. Thanks!


This is actually a common question. I know technicians with years of experience that still have trouble telling the difference between crossover and straight-through cables. Even though they might look the same, the wiring in crossover and straight cables is different. One doesn't perform any better then the other, except to say that in some situations one cable will function where as the other type won't. The reason for this is that the two types of cable have different purposes for different LAN configurations.

For example, the following connections will typically require a crossover cable:

  • computer to computer
  • computer to uplink port
  • computer to print server
  • uplink port to uplink port (hub/switch)
  • normal port to normal port (hub/switch)

Whereas in these situations you would use a straight-through cable:

  • computer to residential gateway/router
  • computer to normal port (hub/switch)
  • access point to normal port (hub/switch)
  • print server to normal port (hub/switch)
  • uplink port to normal port (hub/switch)

If you're unsure of what cable to use in a given situation the general rule of thumb is "If there is a link light, the cable is right." So, just in case, always have both on hand.

Positive ID
Identifying a straight-through cable from a crossover cable is actually simple. The main way to tell the difference is to compare the wiring order on the ends of the cable. If the wiring is the same on both sides, it is a straight-through cable. If one side has the opposite wiring, meaning that the cables in pin positions 1, 2, 3 and 6 have been crossed over, then it's a crossover cable — hence the name.

When trying to identify a cable, you should look at the end of the RJ-45 cable with the clip facing away from you. Brown is always on the right and Pin 1 is on the left. A crossover has one end with the orange set of wires switched with the green set. The color-coding specified within the clip is defined as EIA/TIA 568A/568B.

You'll find more detailed information on these specifications along with instructions on how to construct your own RJ-45 cables and detailed illustrations of the crossed cables here.

It might also be helpful to note that many new network devices come equipped with auto-sensing ports that automatically configure themselves to work with whichever cable is connected to them. So, fortunately, you shouldn't run into this problem too often.

I have two computers in my home office. One is a Dell Dimension desktop PC and the other is a Sony VIAO notebook I use when traveling. Both systems run Windows XP Professional. For Internet access I have Time Warner's Road Runner cable service, and I use Microsoft's Internet Connection Firewall (ICF) and Internet Connection Sharing (ICS) to share this connection between my PCs. To protect me from viruses, I have anti-virus software installed on my Dell system.

The other day I was showing one of my co-workers something on my notebook and he notice that I didn't have any anti-virus software installed it. I tried to explain to him that I don't go on the Internet with this system when I'm not at home and that when it's connected to my home network, the software on my Dell system protects it. No matter how much I explained it, he still insisted that I needed to install the anti-virus software on all of my systems.

I was under the impression that if the anti-virus software was installed on the computer with the Internet connection then that would be sufficient to protect any other PC on my network. However, since we had this discussion, I'm not sure.

Is it really necessary for me to purchase and install another copy of AVG on my notebook if I already have the anti-virus software protecting the PC that the Internet traffic is coming in on? Thanks!

This is a question we run into a lot: Your friend is 100 percent totally and completely correct. Even though only one of your PCs is directly connected to the Internet, both of your systems have Internet access and both systems are capable of accidentally downloading or opening virus infected files. For that reason it is absolutely imperative that you install a good anti-virus package on ALL of your systems.

It sounds to me like you might be confusing the role of your anti-virus software with the role of a firewall. Both protect you, but in different ways. The anti-virus software protects your PCs from becoming infected with troublesome and sometimes destructive viruses. It does this by being installed on each individual PC, and it monitors all the activity that takes place on that PC in real-time.

The firewall, on the other hand, protects your entire network by monitoring the Internet traffic attempting to gain entry into your network through your gateway (i.e. your cable modem). Since all the traffic needs to pass-through the firewall before being given clearance to enter the network, all of your PCs are protected from any possible threats. This is what prevents intruders or hackers from accessing your personal information or from participating in a Denial of Service Attack on another company's Web site.

The reason for the difference is simply because the threat is only coming from one source; your Internet connection. A virus on the other hand can get onto your system through multiple sources. Whether that is an infected e-mail or something accidentally picked up through a file swapping service like KaZaa. So bottom line — get the anti-virus installed onto your system ASAP! Good Luck!

Adapted from PracticallyNetworked.com, part of the EarthWeb.com Network.

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