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Server loses Internet connection

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by bowieb

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I have an NT 4.0 server that is losing it's Internet connection on a regular basis.

When this happens, the computer can connect to computers in the local LAN and even ping past the firewall to our external router, but pings or other connection attempts to anything on the Internet will time out. Other machines on the same subnet can connect to the Internet without any problems. Sometimes rebooting the machine will fix the problem, but sometimes I just have to let it sit for 10-20 minutes until it decides to start connecting again. This computer is our email and proxy server, so it causes a moderate amount of disruption when this occurs.

A tracert from the system will show our internal router and our external router, but the router from our ISP times out. A tracert from another machine on the subnet looks normal.

This system is running:
NT 4.0
IIS from the NT 4.0 Option Pack
MS Proxy Server 20
MS Exchange 5.5

Does anyone have any ideas?

Bowie

11 replies

by allen610

I'm assuming with proxy and exchange on the same box you are running 2 network cards on this system. What you should try is when it goes down, see if you can ping the outside card from that box. From what you have described so far it sounds like to me you might have your outside network card going bad. Have your other internal machines try and ping the outside ip address on that card and see if it will respond. If it doesn't respond I would check your event log to see if there are any errors there about your nic. Are you just running TCP/IP protocol or are you running multiple?

thanks
al

by bowieb

There is only one network card in the machine. The firewall is configured to allow this system to have external access vi a static IP translation.

by bowieb

This system is on a Private IP subnet. It connects to an internal router which forwards packets through the firewall (Which does a static IP translation) to an external router. The external router is connected to a T1 line.

by astute

Hi,

I had faced similar problem with a NT Server 4.0 with 2 ethernet cards, The only Mistake was that I had assigned 2 different Gateways for each ethernet card, After deleting one gateway IP ( leave it blank) it worked fine.

May be this willhelp u.

Good luck!!!

by jerrym mcse+i / a+

Hi Bowie,
you stated that other machines can connect to the internet when these others can't, but you didn't specify the type of clents, Proxy depends on wins resolution to work, next time you experience the issue,
1. from the client machine ping the proxy server by name..did that work? (probably not), if not, add a lmhosts file with an entry for the proxy machine, ping proxy by name, did it work? if yes, then the client machines network configuration for entries relating to the wins server, if using dhcp then using winipcfg or ipconfig (depending on plateform) ensure the dhcp server is aware of the wins server addresses... let me know if this doesn't help...
thankyou for your post! jer

by bowieb

The problem is occurring with the proxy server. The clients are affected (obviously), but that is not where the problem lies. If the server can't access the Internet, then the clients won't be able to either. I only mentioned the proxy software in case it might be contributing to the problem.

The other machines that I am testing are in the same subnet as the proxy server and have a direct internet connection the same as the proxy server.

Basically, I've got two machines in the samesubnet with identical TCP/IP configurations (except for the IP address). One stops connecting and the other keeps on going.

The strange thing is that this only affects addresses outside of our LAN. I can still access anything on our local lan (including the other subnets and both DMZs on the firewall).

by mpdcsup

Hi Bowie, I've been following this post since Friday. How many NICs are installed in the machine? Has this been a problem all along, or is it a recent phenomenon? If it worked before, has anything changed with the network topology? with the ISP? the DMZ?

One of the big obstacles you have to overcome in your troubleshooting is determining all of the possible causes for the results of tests you make (like pinging).

What makes the task on this machine more daunting than on the others is that it's running Proxy and making an assumption about the ip address presented to a remote host (say an external router) is not as reliable as the same assumption on a normal IP stack implementation (like on a client).

A few key areas of the computer's configuration to study (in dizzying depth) are the routing tables, LAT, and DNS (if you're not completely using IP addresses for testing).

by bowieb

There is only one NIC in the machine.

I'm not positive about exactly when this started. It's an intermittent problem and I only took over the administration recently. Generally, the problem only occurs once every week or two and then only lasts10-20 minutes or so before it goes away on it's own.

The network topology has been completely re-arranged. I don't remember exactly how it worked before, but this is what it looks like now: These computers are on a switch VLAN. To get to the Internet, they have to be routed through an internal router, a firewall, and an external router. (When the problems occur, I can still ping the external router)

The routing tables look fine and the DNS is working. I'm not familiar with LAT.

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