Billion BiPAC 7800(N)X(L) User Manual page 88

In group "test", P2 and PPP0.1 are grouped in one group, they have their only network , see LAN.
If you want to remove the group, check the box as the following and press Remove.
Note: If you like to automatically add LAN clients to a WAN Interface in the new group add the
DHCP vendor ID string.
By configuring a DHCP vendor ID string any DHCP client request with the specified vendor
ID (DHCP option 60) will be denied an IP address from the local DHCP server.
If a vendor ID is configured for a specific client device, please REBOOT the client device
attached to the modem to allow it to obtain an appropriate IP address.
Each LAN interface can only be added into one group and one WAN interface can only be
used in one group.
83