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I'm beginning to deploy a Windows Server 2008 R2 in my organization and I'm running on some problems. Right now, all connections to the server fail because the computers cant connect to the server. While trying to diagnose the problem I discovered that if the server was pinging the client computer, then the connection worked perfectly. But if I tried that when the server was not pinging the client, the connection would time out.

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It sounds like an ARP issue, where the client (or, if routed, the server's gateway) asks for the server's hardware address and gets no response, but if the server asks for the client's address, it gets a response; once the ping comes through the client caches the server's hardware address.

The question is, what the cause is. Network topology issues like looping with no spanning tree would be likely - does that give you enough to go on, or can you give us a quick run-down of the network connection between the server and the client (Same subnet or different? How do the switches connect? Any vlans?)

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The network structure is very simple. We have a Netgear Router connected to the Internet. To that we have a Cisco Unmanaged Switch and connected to the switch is a Wireless AP. Both computers are in the same subnet and the client is connected to the Switch while the server is currently connected using a Wireless Card to the WAP (For production is going to be connected to the switch directly, I'm only using the WiFi option while configuring) – Carlos G. Mar 25 '11 at 22:51
@Kiranu Huh. Unless there's an extra wire connecting the AP to the switch, then that doesn't explain much, and the unmanaged switch won't help with troubleshooting. Try pinging the server and then run arp -a - check if the server's IP is listed. If not (probably not), then using Wireshark to watch the ARP conversation is a good next step. – Shane Madden Mar 25 '11 at 22:59
Let me try that... Thx – Carlos G. Mar 25 '11 at 23:24
If you have a loop in your network, then in a few seconds you will have a broadcast storm. No other traffic will be able to pass. You should rule out a looping issue. – Mircea Vutcovici Mar 26 '11 at 3:09

Are you sure the server isn't disabling the network adapter when it's inactive for power conservation? If the server and client are in the same subnet there shouldn't be an issue with communication. Especially considering you can ping the server when the server is pinging the client. Can you replicate the issue using another client?

To check go to your network adapter's properties then click the "Configure" button and move to the "Power Management" tab. If it is checked, uncheck the "Allow the computer to turn off this device to save power".

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