We have a Vigor 2865 and used to have no issue with network resolution from LAN 1 to LAN 2, but for some reason it is not working anymore.

Since this website is soooo backward that it won't allow images to be inserted or attached, I'm not going to provide one, but in the LAN > General Setup page, both Lan 1 and Lan 2 are ticked in the lower table. I can not see why there is not network resolution from LAN 1 to LAN 2.
 

Hi  Rob ,

Is it happening from both LANs, or only one side, and if so, is it all devices or only some/one?

Have you implemented a Firewall rule recently that might’ve blocked the flow of traffic, or an Object change that has affected a ‘Pass’ rule possibly?

This can also occur when the gateway address isn’t set correctly on the device(s), as having the wrong gateway address means the LANs can’t find the route over to the other LAN.

Other possibilities could be a router config restore (corruption), if you have restored it recently, or even upgraded it to a newer model and restored the older/other model’s config onto the new router?

It could also be a firmware update issue?