FireBrick Bonding more than 3 lines
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 separate VLANs on the appropriate ports, and on the FireBrick, the <ppp .../> config would have VLAN="n".