I'm having a strange issue with one of the networks I manage recently. We have about 14 different networks connected together through a Netgear hardware VPN. Everything has been running fine (other than standard connectivity problems) for a few years now, but I've hit a wall with a problem that's just cropped up at one of the VPN endpoint locations.

Our primary VPN network is on the 192.168.1.0/24 subnet and our other 13 networks are on the 192.168.2.0/24 - 192.168.14.0/24 subnets. We run a terminal server on the 192.168.1.0/24 network with IP address 192.168.1.100. Starting Thursday of last week, we had a problem with connectivity of the 192.168.2.0/24 network to 192.168.1.100.

When troubleshooting the problem, I found that Network 2 (192.168.2.0/24) still had connectivity to the Internet as well as VPN connectivity to Network 1 (192.168.1.0/24). We could ping and connect to any other device other than the server with IP address 192.168.1.100. Also, none of our networks had an issue accessing 192.168.1.100.

I ran a scan on Network 2 after assigning static IP addresses to one of the workstations but received no response from 192.168.1.100 (looking for possibly a new device that someone had plugged into Network 2 that had a duplicate IP address with the server). Asking the staff, noone had reported connecting a new device to Network 2 as well.

I then assigned a secondary IP address of 192.168.1.88 to the server and could ping and connect to the secondary IP address from Network 2, but still couldn't access it via 192.168.1.100. I then just rebooted the Netgear VPN Firewall (FVS318v3) and after it came back up, connectivity to 192.168.1.100 was restored.

Beforehand, when checking for devices with a possible duplicate IP address, I did run a check for available wireless access points and stations and found none (our wireless is secured via MAC address access control through a WG102 device). I thought that it may have been a fluke for some reason since everything came back up after a power cycle of the VPN Firewall. Things ran fine for a few days until this afternoon, when the problem happened again.

One of our users claimed that they had connectivity problems to the server and after connecting to the computer, I found that I couldn't ping the server address anymore. I could still ping the alternate IP address of the server though, so I went ahead and rebooted the VPN firewall again and connectivity was restored.

Unfortunately, I can't find anything in the security or VPN logs of the firewall that helps point me in the right direction, so I thought I would go ahead and ask to see if anyone else has any other insight into why we've started having this problem. I am aware that it could still be a device with a duplicate IP address of the server on Network 2, but every employee claim states that there's been no such new device brought in to the network.

I know this is a long read, but any help is appreciated!

Thanks,

Justin