PChucks Network: Connecting Two Computers With A Crossover Cable

Most of my articles in this website are about Windows Networking / File Sharing, or about Internet Connectivity, and start by assuming that you have several computers, and a hub (router / switch) connecting them. But what if you have just 2 computers, and just want to quickly move files between the two? Or maybe you want to setup Internet service, for the 2 computers, without using a router to share the service?

You don't always require a hub (router / switch) to connect just 2 computers.

Make The Right Decision
Use The Proper Equipment
Setup The Network - No Internet
Setup The Network - With Internet
Verify The Network
Troubleshoot The Network, If Necessary

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Make The Right Decision
Start by asking yourself - what do you want to do - both now, and in the future? If you just want to immediately connect just these two computers, and quickly move files between the two, without Internet service, then this is the right start.

If your future might include Internet service, or if you might end up with a third computer, then you would really be better off using a hub (router / switch).

If you want to connect the two computers, and share Internet service, you can do that using a crossover cable. But know the issues before you start.

If the computer with Internet service has it thru a dedicated modem, either:
- Internally installed.
- Connected externally, but thru a serial cable.
- Connected externally, but thru a USB cable.
If the computer with Internet service has it thru an Ethernet connection, or thru WiFi, then this is not a valid solution. If the Ethernet or WiFi connection is on subnet 192.168.0/24, this will not work at all. In the latter case, you will have to connect both computers directly to the LAN with subnet 192.168.0/24. If the Ethernet or WiFi connection has a private LAN address (10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/24), you're behind a NAT router, and you should setup a bridge, rather than use ICS.

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Use The Proper Equipment
The simplest solution, for networking just 2 computers, is to get an Ethernet crossover cable, and connect the two directly. A single crossover cable is the equivalent to getting a hub (router / switch), and a pair of straight-thru patch cables.

Please use Ethernet, not Firewire or USB, for connecting your computers. Firewire / USB networking requires extra drivers, and extra work. Ethernet drivers are native in all modern operating systems.

Please use a Cross-over Ethernet cable. A Straight-Thru, aka Patch, cable may work for some newer systems, which can automatically sense the need for a cross-over. But a cross-over cable will work all of the time, when you need to connect two computers directly.

Patch cables may come in many colours and lengths; some computer stores will have dozens of choices to suit your cabling needs. Cross-Over cables, when you find them in the store, will be explicitly labeled "Crossover", and will come in one colour (probably orange), and one length (probably 3 or 5 foot).

Please buy a properly made cross-over cable. If you're a masochist, or extremely desperate, you may make your own from a pair of patch cables, properly spliced. But Ethernet cables, that support modern high speed networks, require precision in their construction. I'm a fan of do-it-yourself activity (as in the reason for this website), when it's properly planned. I don't recommend do-it-yourself Ethernet cabling, when you're setting up a network. Buy a cable, unless you're very experienced with networking and can easily recognise the possible problems.

If you replace the two Ethernet adapters, one on each computer, with two WiFi adapters, you may be able to eliminate the Ethernet cable and setup an ad-hoc WiFi network. A WiFi based ad-hoc network isn't terribly different from an Ethernet based ad-hoc network, once you get the WiFi connectivity working.

Use the Device Manager in Windows, and test the network adapter in each computer. Connect your cross-over cable to the two network adapters. Observe the lights on the network adapters, and / or the status indicated by the Local Area Connection icon in the tooltray - do both computers indicate successful electrical connection?

Now, will you be setting up your network to Share Internet Service? Or just to share files, with No Internet Service?

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Setup The Network - No Internet
If you just have two computers, and no Internet service to either, run the Network Setup Wizard on each computer. Select the last option

This computer belongs to a network that does not have an Internet connection.

Having connected the two computers physically, and checked that you have no physical problems, you need to make the logical (TCP/IP) settings. If you have Windows XP / Vista, or other current operating systems on your computers, you're in luck. Modern operating systems use a system called APIPA, and should be able to provide ip settings automatically, so the two computers will connect to each other. If you allow the two computers to dynamically assign addresses, APIPA should take care of this for you.

Be prepared to get an error message - Limited Or No Connectivity - if you use APIPA configuration.

NOTE: if any of your computers are NOT running Windows XP / Vista, you'll have to set the IP address and subnet mask manually, on those computers. Remember IP addresses have to be unique for IP addressing to work.

Run "ipconfig /all", from a command window, on each APIPA compliant computer first.
Make a list of which addresses are automatically assigned.
Manually configure each non-APIPA compliant computer.
- Set each computer up with a unique IP address, in the 169.254.x.x subnet (written as 169.254/16 in many cases).
- You assign IP addresses using the TCP/IP Properties wizard. Select "Use the following IP address". Only worry about IP address and Subnet mask - the other settings are only useful if you have an outside connection. With locally connected computers, just IP address and Subnet mask are essential, and should be assigned as described above.

Having connected the two computers physically, and checked that you have no physical problems, next Verify The Network - make sure that it works properly.

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Setup The Network - With Internet
If you have two or more computers, with Internet service to one, and wish to share the service to the others, run the Network Setup Wizard, first, on the computer that has Internet service. Select the first option

This computer connects directly to the Internet. The other computers on my network connect to the Internet through this computer.

You'll probably be running ICS on this computer. Note the disadvantages and requirements of ICS, and a possible alternative. You'll have to have two separate network connections (one might be a modem, directly or internally connected). You'll indicate which connection provides the Internet service, and then which connection(s) are to be used for sharing the Internet service.

If, per the ICS alternative, you decide to use a bridge, remember that both of the network adapters, on the bridged computer, will have the same IP address. Plan your testing accordingly.

If you decide to use ICS, run the Network Setup Wizard on the other computers, and select the second option

This computer connects to the Internet through another computer on my network or through a residential gateway.

If you can't run the Network Setup Wizard on any computers, use the TCP/IP Properties wizard, and select automatic configuration.

If the second computer will be running as a server, and providing data to the Internet, remember that the ICS server will have to be online constantly. Having dealt with that requirement, setup the ICS server to (KB231162): forward the right ports to the Internet server.

Having connected the two computers physically, and checked that you have no physical problems, verify that the network works properly.

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Verify The Network
Please verify that you have connectivity between the computers first.

Run "ipconfig /all" on each computer, from a command window. Note the IP address and subnet mask for each network connection.
Make sure that you don't have a bridge, on any computer, unintentionally.
Verify that all computers are on the same subnet, and that each has a unique address.
- If this is two computers without Internet service, each computer should have an address of 169.254.n.n, and a subnet mask of 255.255.0.0. This will indicate that each is on subnet 169.254/16.
- If this is two, or more, computers sharing Internet service, the first computer (thru which the others will be getting Internet service) must have an address of 192.168.0.1, and a subnet mask of 255.255.255.0 (on the connection used for sharing the Internet service). All of the computers getting Internet service thru the first computer must have an address of 192.168.n.n, and a subnet mask of 255.255.255.0, and show both DHCP and Autoconfiguration Enabled = Yes.
From each computer, again in a command window, ping the other. If, for instance, the address on Computer B is "169.254.1.2", open a command window on Computer A, and enter:
ping 169.254.1.2

If you get back a series of responses like
Reply from 169.254.1.2: bytes=32 time<1ms TTL=128
Reply from 169.254.1.2: bytes=32 time<1ms TTL=128
Reply from 169.254.1.2: bytes=32 time<1ms TTL=128
Reply from 169.254.1.2: bytes=32 time<1ms TTL=128

then you are ready.

When you open Windows Explorer on each computer, and look in Network Neighborhood, you should see both computers. And when you open (doubleclick on) one entry, you should see the folders and files.

And, if the computer directly connected to Internet service can access the Internet, the other computers should be able to do so also.

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Troubleshoot The Network, If Necessary
So what if it doesn't work, per the basic testing above? Well, now you start troubleshooting, and methodically, in the right sequence.