I have a network using an M4100 switch connected to an EdgeRouter Infinity. I'm also connecting to the EdgeRouter over PPTP for configuration and testing purposes.
I've created VLAN 80 on the M4100 and tagged the uplink port for VLAN 80. The uplink port goes directly to eth0 on the EdgeRouter and has firewall rules set for providing DHCP/DNS. The services are working perfectly and the M4100 is able to receive an address and resolve forwarded DNS from the EdgeRouter.
The problem I'm having is that when I add VLAN 80 as a sub-interface to eth0 I immediately lose contact with the M4100 until the VLAN is disabled. I've tried applying an IP to the VLAN interface itself (both being the same as the physical interface, another subnet, as well as just leaving the virtual IF subnet undefined) but the result is the same.