Network Switch

[Gavin Scott]

Howdy.

I have a laptop, a rebuilt PC and one cable modem. I don't often use them together so just swap the ethernet cable between as and when required.

However, I've managed to get my hands on a little Belken 8-port network switch.

Its labelled on the rear with ports 1 thru 8. Connecting the ethernet from the cable modem to port one, and the pc to port two allows the net through no problem. Connecting the laptop to port three tells me I have limited connectivity.

Both machines are set to the same workgroup of MSHOME.

What do I need to do to make both work simultaneously? I've never used a switch before.

[Nick Harvey]

Others will, hopefully, come up with more detailed advice, but the first thing to check when you introduce a switch is where you're using straight (sorry to use that word on here) cables and where you're using crossover cables.

You have to get the right ones in the right places.

Try swapping the cable you're using for the PC with the one you're using for the laptop and see if the problem moves to the PC.

[Gavin Scott]

Others will, hopefully, come up with more detailed advice, but the first thing to check when you introduce a switch is where you're using straight (sorry to use that word on here) cables and where you're using crossover cables.

You have to get the right ones in the right places.

Try swapping the cable you're using for the PC with the one you're using for the laptop and see if the problem moves to the PC.

Thanks Nick.

Doing what you suggest does move the problem (and connectivity) from one machine to the other.

I know I have one crossover cable, but the rest I am sure are non-cross ( ). It may be that the cables are a bit knackered - as I've certainly added a couple to my collection before.

If we assume its a cable fault - am I right in thinking plugging up with good cables as described in my opening post should work without any other configuration required?

[Sput]

Ah, cable modems can only support one client. What's happening is that it'll assign the latest machine to appear on the network an IP address and give that one the internet access, leaving the other machine to wallow in self-pity. If you want to share the modem properly you'll want a router. The other potential problem is that you're relying on the modem to hand out IP addresses. If you want the computers to talk to each other you'll have to assign them manually.

[Gavin Scott]

Ah, cable modems can only support one client. What's happening is that it'll assign the latest machine to appear on the network an IP address and give that one the internet access, leaving the other machine to wallow in self-pity. If you want to share the modem properly you'll want a router.

Raspberries. I'll return it to the nice person who gave me it then.

The other potential problem is that you're relying on the modem to hand out IP addresses. If you want the computers to talk to each other you'll have to assign them manually.

I've just gone back from Vista to XP pro, so I could run the wizard to connect them I guess. The laptop has a docking station with an extra ethernet port.

Should I use straight through cat5 cables or one crossover and one straight?

[cwathen]

First thing to establish is whether or not you have a router or a hub. Although they might look the same, they are technically very different. A router is capable of internally directing specific traffic around to specific ports, so that the device on the end only has to deal with the traffic intended for it. A hub is a much simpler device, being little more than a multiway adaptor which simply takes whatever is sent in and sends it out again to every port without any internal routing ability. A lot of cable modems cannot work without a proper router.

But, assuming your equiment can work, to expand on Nick's explanation, 'Crossover' cables (where one of the connectors has two wires swapped around) are usually only used to directly connect two computers together via their ethernet ports. Sometimes older cables modems (where they assumed you'd connect directly to the PC) also use them to connect to a switch. Some switches also use them to connect to other switches. Generally though, modern equipment is all designed to use 'straight through' cables (where the wiring is the same at both ends) exclusively.

If you have connectivity problems and have a crossover cable in use with modern equipment (easy to tell - just hold the two connectors next to each other in the same orientation. If the conductors are connected in the same order on both, then its a straight through, if two of the conductors are swapped around, then its a crossover) it's usually best to assume that this is wrong unless you specifically know that such a cable is required.

If you establish that the wiring is OK, the next thing to check is that both computers are set to assign IP addresses automatically (the operating systems will request an IP address from the router or modem) to ensure no clashes. If the OS is set to 'force' an IP address (arbitrarily using a user-specified address regardless of whether or not it's valid) then it's possible that it's clashing with something else. To check this in Windows 2000/XP go to Network connections, pull up the properties for the connection you're using (usually 'Local Area Connection' if its hard-wired) Scroll down to 'Internet Protocol (TCP/IP), click properties, and check that 'obtain an IP address automatically' is selected. (note, with some older modems you do specifically need to set each address manually in order for it to work, in this case, check the 'specify an IP address' option and enter a unique address for each machine. The accepted practice for home/small business networking is to use the 192.168.x.x range, with your first machine 192.168.0.1, the second 192.168.0.2 etc) and a subnet mask of 255.255.255.0 on all machines.

If the network settings are OK, then the final thing I can think of to try (clutching at straws now admittedly) is to pull up a command prompt (start/run/cmd) and enter the command 'ipconfig /release'. This terminates all active TCP/IP connections and releases the IP address used for other programs. Once in a blue moon, something has gone awry with the networking software itself and this command effectively gives it a kick up the arse which gets it going again.

[Sput]

Oh and with the crossover vs cat5 thing, most hubs/switches/routers don't mind which you use, but you need a crossover to directly connect two computers.

[Gavin Scott]

Oh and with the crossover vs cat5 thing, most hubs/switches/routers don't mind which you use, but you need a crossover to directly connect two computers.

Ok, so modem to ethernet 1 on laptop, and crossover from ethernet 2 on laptop to pc.

[Sput]

Yep, and if you like you can set up internet connection sharing on the laptop so the pc can access the internet via the laptop as well.

[Ebeneezer Scrooge]

First thing to establish is whether or not you have a router or a hub. Although they might look the same, they are technically very different. A router is capable of internally directing specific traffic around to specific ports, so that the device on the end only has to deal with the traffic intended for it. A hub is a much simpler device, being little more than a multiway adaptor which simply takes whatever is sent in and sends it out again to every port without any internal routing ability. A lot of cable modems cannot work without a proper router.

That's not strictly true, that's the difference between a network switch and a hub - the network switch being the intelligent device that can learn what is on which port and the hub being a dummy device which just sprays packets out to all available ports.

A router, strictly speaking, is a 2 port device that bridges 2 networks. One port for the WAN and one port for the LAN (obviously it can be used for other purposes too). Use of routers means that less global ip addresses are required as the network on the LAN side is separately administered from the WAN side.
In domestic units, routers are generally sold with integrated hubs allowing you to connect more than one machine/switch to the router, which often muddies the water in explanations of the differences between routers, hubs and switches.

As was previously mentioned, Gav's problem is more than likely to be down to not having a router to isolate (and link) his domestic network from the wider cable network.

[Gavin Scott]

Crossover cable bridged the 2 computers perfectly.

Ta for all the help.