Case Studies

Bonding VDSL and ADSL

The Challenge

In many locations, the total bandwidth offered by a single broadband line is insufficient to be useful.

This could be because extremely high bandwidth is required (for example, for transmitting large video files from place to place) or because the premises is located far away from any high bandwidth connectivity (for example, on a farm a long distance from the local exchange).

In both these scenarios, multiple lines may be installed and combined together.

Andrews & Arnold wished to launch a bonded solution package (including FireBrick, line rentals etc.) for one monthly fee and call it "Office::1".

The Solution

Bonding with the FB2900 is very straightforward. With an ISP who can support it, simply configuring egress rates on two interfaces is enough; literally two settings in the configuration of the device. The FireBrick does per-packet bonding, and sends the packets down the two (or more) links in ratio with their configured egress rates. This means that a single stream of TCP (for example a single threaded FTP transfer) can use all the upstream bandwdith. In the opposite direction, the FB6000s at the ISP handle the bonding, dynamically setting egress rates utilising the sync rate passed via the L2TP from the wholesale provider.

More Info

A note on the distinction between "true bonding" and "load sharing"

Load balancing or load sharing is a technique used by other devices, and indeed can be configured on the FireBrick. But it is generally an inferior technique, since it randomly allocates sessions over two or more links on a per session basis. This means a single TCP session transfer cannot utilise all the links; only being able to use the capacity of one. It can still offer load aggregation, especially if there is a large number of client devices, all needing access. But it's technically inferior in most cases. The FireBrick does true "per packet" bonding.

FB2900 Bonding multiple VDSL and ADSL circuits

Features Used



Simple 'dumb' VDSL and ADSL modems connect to the FireBrick and the FireBrick connected to the ISP via PPP as normal.

Tunnels (100)


Optionally, L2TP can be used over a 3G or 4G data SIM connected via a USB dongle for further fail over scenarios.



Profiles can change much of what the FireBrick does based on time, pings and so on. In this case, profiles monitor the PPP and fail over to ADSL or a 3G/4G dongle as required.



IPv4 and IPv6 firewall rules are in place

(All the network diagrams on these case study pages are very rough representations and are not an accurate representation of live networks)

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