intermittant connection problem with home network

We have 3 computers, all running WindowsXP pro in a home office, all in the same room. We have a T1 LAN line coming in, connected to a D-Link switch. Each of the 3 computers is connected to the switch. Each computer has a gigabit network card. All 3 are using ZoneAlarm Internet Security Suite 7.xx as their sole firewall (however, the problem occurs even with all 3 firewalls disabled)

The problem is this:
The computers often cannot see each other, sometimes losing connection in the middle of a file transfer, giving a "this network resource is unavailable" error message. Usually, opening up the offending computers connection icon and clicking "repair" solves the problem - but only until the next time they lose connection. Basically, it's a **** shoot any time we try to access another computer via "my network places" sometimes it connects, sometimes it doesn't.

When we exchange the switch for a router, we don't have this problem, however, we lose the individual IP addresses each computer has (our ISP gives up to 4) so this isn't really a great solution.

I recently tried mapping the network drives, but I don't think it has made it any easier to connect. It still works sometimes and not others.

Obviously, we have checked all the physical connections and swapped out network cards, cables and even the switch but nothing seems to solve the basic problem.

Does anyone have any ideas on what the problem is and if it's solvable without having to lose our individual IP addresses?

 

I'd go for an auto-negotiation problem as being the most likely candidate.

Modern network equipment can automatically determine the best network speed and media type (duplex or half-duplex) to use. To do this the a network card will try to connect at it's fastest speed. If it is able to communicate with the network device it is connected to (hub, switch, router, or another network card), then it will use that speed. If not, it then drops to the next slowest connection type and tries that. It will continue to do that until it finds a connect that works. This process is auto-negotiation.

Sometimes auto-negotiation becomes unreliable. When that occurs a connection can fail and the NIC and/or network device will try to go through the negotiation process again, often taking some time to get the right speed and duplex combination.

The simple fix is to manually configure the network connection speeds and duplex. You can usually do this via the Advanced tab on the Network card properties. If you have a managed switch you can also do the same at the switch end.

The more expensive solution is to replace the switch. I'd only do this after ascertaining that this diagnosis is correct by testing that the problem is fixed by using static mapping, or if I detected the problem via another method (high amounts of error packets).

Also gigabit connection is going to be more susceptible to noise and/or cable problems. So dropping the speed to 100Mb/s might give you a more reliable connection.

BTW - full duplex is faster than half duplex.