I have a strange one. This is with two 2011UiAS-2HnD.
LivingRoom 192.168.1.24 (spf1) -> (spf1) BatteryRoom 192.168.1.25
The BatteryRoom router is doing most of the work. Duel WAN, VLANS, VPNs, etc. The LivingRoom router is working as a WIFI access point, and some of the ports are assigned VLANs, but that is it.
When I plug a laptop into port 5 of LivingRoom, it is on VLAN3, gets a DHCP address from the VLAN3 (192.168.3.0/24) pool (on BatteryRoom router), and everything just works fine.
When I plug the same laptop into port 2 of LivingRoom, it is on VLAN4, gets a DHCP address from the VLAN4 (192.168.4.0/24) pool (on BatteryRoom router), and it can access the internet, but within seconds, nothing else can ping BatteryRoom at 192.168.1.25. Everything else goes down. I can ping things in the 192.168.1.0/24 subnet, even stuff connected to the BatteryRoom router, but I can't ping the router itself. BatteryRoom router itself at 192.168.1.24 can't ping BatteryRoom at 192.168.1.25.
Unplugging the laptop from port 2, and after 3 minutes or so, I can ping 192.168.1.25 again and everything returns to normal.
I don't see a difference between VLAN3 and 4. It's like an MAC address collision, but I checked the ARP table and the MAC address on the laptop, and it is not the same as anything on the 2 routers.
Anyone see something like this before?
Sanitized configs attached.