FireBrick Bonding more than 3 lines

Overview

A FireBrick 2x00 has 4 ports, a typically one port will be for the LAN connection, and the rest for connections to the ADSL modems. As there are 4 ports are we restricted to only bonding up to 3 ADSL/FTTC lines? no.

To overcome the physical port restriction a VLAN switch can be used, eg:

ADSL MODEM 1 --
ADSL MODEM 2 --
ADSL MODEM 3 --  VLAN Switch -- Firebrick -- LAN
ADSL MODEM 4 --

The switch would be set up for 4 (or more) separate VLANs on the appropriate ports, and on the FireBrick, the <ppp .../> config would have VLAN="n".