I manage a spoke-and-hub network of 30-some sites, almost exclusively with SonicWall routers. We recently brought in a new location, which had been using a UniFi gateway.
The new location’s network ended up being on the same subnet as one of our existing locations, so I re-did the existing location on a new subnet (less stuff to change) and updated the VPN. Everything is working fine for them.
I was able to get a VPN going to the new location, but found in the process of installing their printers on a central server that most of their printers would drop offline except for ping (but only over the VPN) for long periods. The printers would still work inside their building, and two would continue to be available over the VPN.
Much troubleshooting was done with the location’s network (Cisco managed switches) and router, which was eventually replaced with another SonicWall, but the issue persists. Before replacing the Unifi router, a 5-port unmanaged switch was placed between it and the rest of the LAN, and one affected printer was connected through it to bypass the rest of the LAN, but it still experienced the same issue.
The affected printers are all Brother units, plus two Epson receipt printers, on ethernet in the location’s network. No security is set in the printers or the switches. One printer was moved to their wireless network, with no improvement. A Toshiba E-studio and a Zebra label printer have no issues staying connected.
The affected printers are all on static IPs (assigned by the Unifi gateway first, now by the SonicWall), with the same gateway and DNS as the unaffected printers.
I’m at a loss as to what could be going on. It almost seems like there’s something in the VPN connection left over from the previously-conflicting store that’s causing issues, but I’ve cleaned up all the old rules and objects that referenced the IP range.
Edit: Thanks for all the suggestions. I ended up finding a post on Spiceworks with exactly the same issue and a solution. The main switch (an L3 Cisco) needed a default route set to point to the other subnet through the local gateway.