Sometimes I get weird connectivity issues with one of our test machines. It's like someone out there is clobbering me on the network. It turns out this is almost always because someone has hijacked my IP. I thought it was because we have so many vmware ESX images. Each one is dished out an incrementing mac address, so if you have two ESX boxes out there, won't there be conflict?
Turns out that's not the problem. Someone has a box that gets a valid IP from the DHCP server, then they snapshot it in the running state. Then they take it offline. Much later, that IP has been dished out to my box. Then they fire up that old snapshot, and since they don't reboot, they're trying to use my IP. Then hijinks ensues.
How to find the guy that stole your IP
Power off your box and ping the IP. If it comes back you have proof that someone else is using your IP. Then run
nbtstat. I've anomonyzed 10.4.001.01, 10.4.002.03, MACHINE_NAME1, and MACHINE_NAME2.
C:\>nbtstat -a 10.4.001.01 VMware Network Adapter VMnet8: Node IpAddress: [192.168.48.1] Scope Id:  Host not found. VMware Network Adapter VMnet1: Node IpAddress: [192.168.71.1] Scope Id:  Host not found. Local Area Connection 3: Node IpAddress: [10.4.002.03] Scope Id:  NetBIOS Remote Machine Name Table Name Type Status --------------------------------------------- MACHINE_NAME1 <00> UNIQUE Registered MACHINE_NAME2 <00> GROUP Registered MACHINE_NAME1 <20> UNIQUE Registered MAC Address = 00-0C-29-8F-2C-9E
Hopefully there is enough info in MACHINE_NAME1 and MACHINE_NAME2 for you to find out who owns those boxes. You can also try
nslookup. If the IP for MACHINE_NAME1 is different then the one it is using then you know that the probelm isn't at the DCHP server (who has told MACHINE_NAME1 to be 10.4.001.05).
C:\>nslookup MACHINE_NAME1 Server: DHCP_SERVER_NAME Address: 10.4.001.04 Non-authoritative answer: Name: MACHINE_NAME1 Address: 10.4.001.05