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Client has a LAN comprising about 8 windows xp professional computers and a windows server machine. My software runs on all 8 and share files stored on the server. A problem has arisen with the network this week whereby some computers cannot access the server, some computers can, some computers can no longer access the internet via a broadband router attached to one of the machines, others can, some can access the internet but when are accessing the internet they lose the ability to access the server for currently open programs (including windows explorer) and these need to be terminated and relaunched to restore connectivity to the LAN. Some computers behave normally. He has had a network guy out who cannot make sense of it and just suggests increased RAM on the server while I know nothing about networks myself but would like to help as it's making my software look bad. I'd be grateful for any suggestions

EDIT NEW INFORMATION (question 17 hours old) :

All the computers were on static IPs already. Changing the 'troubled' computers to "Automatically obtain an IP address" today seems to solve the issues. I did this via a remote desktop program so I'm not sure but it appears that communication to the server might have slowed slightly. The server is running Windows server 2003. Does this info give you any clues as to what happened? BTW even when 2 computers were down I was able to go from one to the other via the remote desktop program.

There doesn't appear to have been any duplication of IP addresses. The subnet mask was the same for all computers (255.255.255.0). The default gateway and DNS server addresses are identical and the same on all computers (both the one that works perfectly in all respects and the others). The Wins Server was blank but once I set a computer to automatically obtain an IP it then got an address there

Network topology as I understand it (could be wrong) : network hub and all computers including server cabled directly to this. Internet access is via a broadband (DSL?) router that is connected to the telephone landline and to one computer. This computer is one of the ones that gave trouble. Thanks for the help

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Too many possible problems. Without knowing the hardware and network topology, it will be difficult to diagnose. –  DanBig Sep 22 '10 at 20:36
    
Thanks Dan, in case it might help, the only unusual event that preceded the problem was an attempt to install mozy to back up some files from the server –  bosco Sep 22 '10 at 20:40
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A network guy who's only suggestion is to increase the RAM in the server. Very interesting. I am not quite sure what that is supposed to fix. Can you post more details, please? Are the client computers configured via DHCP? What's the DNS configuration? What device is used to access the internet (gateway, router, ...). The more data you can provide, the better we can help you. –  wolfgangsz Sep 22 '10 at 20:41
    
Depending on the bandwidth available, and the LAN hardware, there is a possibility of Mozy choking the network and causing the network oddities. Try disabling that for a day, and see what happens. –  DanBig Sep 22 '10 at 20:41
    
@wolfgangsz I think I will need to go and look some stuff up at the site as I don't have enough information to give you at the moment. –  bosco Sep 22 '10 at 20:45
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2 Answers

up vote 0 down vote accepted

Two areas you need to check. Start with DHCP, followed by DNS. The description does sound to me more like a DHCP issue. As each machine loses its lease it will exhibit exactly the behaviour you have described.

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Thanks for your answer. All the computers were on static IPs already. Changing the 'troubled' computers to "Automatically obtain an IP address" today seems to solve the issues. I did this via a remote desktop program so I'm not sure but it appears that communication to the server might have slowed slightly. The server is running Windows server 2003. Does this info give you any clues as to what happened? BTW even when 2 computers were down I was able to go from one to the other via the remote desktop program –  bosco Sep 23 '10 at 13:43
    
@bosco, I recommend installing and using DHCP on that server. You'll find it not only avoids a lot of problems but helps to reduce your workload. What you describe in you comment can be attributed to those two computers having IP addresses in a different subnet to the rest of the machines, which is the same thing that happens when DHCP enabled machines are unable to renew their leases. –  John Gardeniers Sep 23 '10 at 21:29
    
Hi john, I think DHCP is already operational because when I switched to "Automatically obtain an IP address" they got new ip addresses different to the previous static ones. Is this correct? I was told that they changed to static ips some years ago after previous network issues which hopefully won't now recur. –  bosco Sep 23 '10 at 22:44
    
@Bosco, DHCP might be running on the router, in which case just use that. –  John Gardeniers Sep 24 '10 at 3:14
    
Thanks John, I gotta lot to learn about this stuff! –  bosco Sep 24 '10 at 9:15
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Too many possible causes here to give a specific answer.

Most common problems:

  • Misconfigurations: check IP addresses, subnet masks, gateway and DNS settings on all computers. Look for duplicated IP Addresses, wrong subnet masks, wrong address/mask combinations (these can very effectively split your network in pieces). If you have an Active Directory domain, all computers should use the server as their one and only DNS server. If you post more informations on your network config, we can be more specific here.
  • Overprotective software: antivirus(es) and firewall(s) can wreak havoc on network connectivity. If you are using them (including Windows Firewall, which is enabled by default) double check their settings, and/or try disabling them for while.
  • Faulty hardware: unfortunately, unreliable switches and routers do exist; try replacing them to rule out a hardware fault. Check also network cables.
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DNS. DNS. DNS. DNS. DNS. DNS. –  mfinni Sep 22 '10 at 21:02
    
Thanks Massimo, I will post a comment when I find out what is the source of the problem –  bosco Sep 22 '10 at 21:09
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take a problem machine and give it a static IP - problem solved? DNS. I love it when people cheap out on network support and then blame random vendors, hoping for free support. –  Kara Marfia Sep 23 '10 at 3:38
    
Thanks Kara. Please see my edit to the question above. I followed your's and others suggestions to put in a static IP but discovered all had these already and it's changing this to dynamic that 'seems' to fix the problem!!! Does this make sense? –  bosco Sep 23 '10 at 13:58
    
Massimo I posted some more information above. I don't know if it helps to explain the situation any further, thanks –  bosco Sep 23 '10 at 13:59
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