During my experimets I found out the MTU below 576 prevents a WAN port from getting IP through DHCP. In my particular case it cut off the remote access to the device as well, so there was a need to go there and set the MTU back to a high value. Also, unlike the old RV042 v1, the new v3 device MTU setting affects the VPN traffic as well. With MTU at 600 the G2G VPN does connect, but the VNC does not seem to be able to work through such a tunnel. The funny thing is such a low MTU settings does not seem to affect VPN connections on old RV042 v1 routers. The currently used firmware is v4.1.1.01-sp.