I pinged the listed Default Gateway on a device, and I received a reply from an IP on a different unrelated subnet. Help me understand how that can happen?

Hi all,

I was troubleshooting an issue on a computer that I was doing support for, and I was having some odd networking issues. There was a different device (a printer) on the network with an IP address in the 192.168.18.X (IP known by looking in the device settings) range with subnet mask 255.255.255.0 in the network (known by ipconfig on the computer). The IP address of the computer I was working with was also in the 192.168.18.X range (known by ipconfig), but was different from the IP of the printer and neither was the network or broadcast address.

So, I attempted to reach the printer IP address via browser, and did not reach it (connection timed out). So then I tried to ping the printer IP from computer but I got this odd response:

Reply from 10.128.128.128 . Destination net unreachable.

Now, I thought this was very odd, because obviously the reply seems to be coming from a completely unrelated subnet. So, using ipconfig, I found that the Default Gateway on the computer was 192.168.18.1. So, the same subnet as the printer and computer. So then I tried to ping the Default gateway's IP and got the same reply:

Reply from 10.128.128.128 . Destination net unreachable.

Now I'm thoroughly confused. Why is the reply coming from this address?

So, I knew users had internet access, so I ran tracert to google.com just to see the path it was using to leave the local network. The tracert went successfully straight through the default gateway's IP address and out to the public internet.

So I don't understand why I was getting the replies from the 10.128.128.128 address when pinging the Default Gateway, but the gateway works fine when using tracert. Can someone help me understand how this might be possible and what I am missing? (FYI, I do not own or manage the network, so I don't have any way to know more than what can be known from the computer)

Thanks!