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Network Keeps Going Down

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by kucster

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Hello I have a SBS 2003 R2 network. 5 XP clients and 1 2003 Stnd terminal server.
I've an issue where all of a sudden the clients + terminal server loose connectivity with the SBS server. It seems to happen sporadically. It started 2/25/09 and did it, 3/11/09,3/19/09,3/31/09,4/1/09,5/6/09. I've replaced the router with a Watchgaurd firebox, replaced the switch, and replaced the Nic in the SBS server. I installed a network monitor and pinpointed the time the network was going down but there are no issues in the SBS eventlog at that time. When it goes down it seems like the clients are unable to resolve DNS names. I was using the DNS on the Firebox but after talking to watchgaurd they said to use the DNS on the SBS server, which I'm now doing.
To be honest with you I'm out of things to check and I don't know where to go from here to solve the problem. Any help would be much appreciated.
Thanks
Sean

11 replies

by brian

Ok, so the workstations are loosing connection randomly to the server, you have replaced the switch, but have you checked the cable running from the sbs to the switch? I have had a faulty cable give me the same problem (just moved the server a slight bit and problems like this started). It may not be the correct answer, but it is where I would go next.

by kucster

Thank you for your quick reply, I forgot to mention that I did replace the network cable that was going from the SBS server and the switch.

by nimmo

I'm not sure of your topology but I guess as a starting point, check to make sure there isn't another DHCP server on the network.

SBS box's will shut down the DHCP service if they detect another DHCP server on the network.

You problem could be that the server is detecting another DHCP server therefore it is shutting down and the other box starts giving out leases providing incorrect IP/DNS/default gateway details.

When you notice this happen again go to a effected PC and do a ipconfig /all and check the TCP/IP details and make sure they are correct.

Also check and see if the server has shutdown the DHCP service.

by kucster

Thank you for your quick reply. The SBS server is not the DHCP server I rely on the router for this role. Could this be causing the issues?

by robo_dev

Ia assume these PCs also connect to the Internet?

when in a failed state:
Can they get to the Internet?
Can they ping the server?

If they cannot get to the Internet, can they surf by IP address? (if DNS has failed).

Are there muliple Nics in the server?

Are you using RAS?

Microsoft has a feature called 'dead gateway detection' which works well, but not always.

Is it possible for a user to create a network loop? Do users have any hubs/switches near them? If you plug a hub into a switch with two connections, it will kill the network in many cases.

by nimmo

Regarding the SBS server not been the DHCP server, this wouldn't be the issue as long as the clients are receiving the correct DNS addresses.

Been an SBS box I'd configure DHCP/DNS and all the other services on that box, it's what SBS was designed for (to allow one central location for all services).

I still think you should check the PC TCP/IP setting when the outage occurs to see what changes have occured so you can narrow this down a bit further.

See what you can and cannot ping either by hostname or IP address.

Even reboot the switch, router, restart the dns service (one at a time though so you can narrow this down)

Can you tell us the layout of the network in a bit more detail i.e.

Do all PC & servers cable from their wall sockets into a patch panel which is then uplinked to a switch which in turn uplinks to the router to the internet.

Do you use a managed switch(s)? If you are using more than one switch for redundancy you will want to enable spanning tree or even just physically remove any redundant links.

by kenone

how many Nics are installed? Is the box checked that says "allow the computer to turn this off", what are the "wake up" params set to?
At the switch, where is it plugged in? Also check the server. When is it going down? Is it random or always about the same time?

by breezer85

... the cleaner unplugs the server to hoover than plugs it back in!!!

Jokes, have you checked the NIC is not faulty, also as mentioned use the SBS for all you DNS/DHCP tasks to see if it resolves the issue!

by wlei24114

Did you check the ip address lease expire time?

by nimmo

Time wouldn't be an issue because once a DHCP lease is up the client will send a DHCP discover packet broadcast to the network and take the first available address offer so it should automatically be receiving a new address.

If there are two DHCP servers on the network then they could pick a wrong address, since this is a SBS domain they would certainly pickup the wrong address because SBS has most likely shutdown the DHCP server once it has discovered another DHCP server on the network.

The issue in this case is easily resolved by removing the second DHCP server, increasing the lease time will just delay the problem.

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