How Does Bonded ADSL Work?

Don’t confuse bonded ADSL with load balanced ADSL.  Bonding involves splitting data up at the packet level, and distributing it across all the available lines on site.  The data is then cleverly put back together again before being sent out to the internet, or to another site within the same network.

This works both ways, for uploading and downloading.  Load balancing ADSL lines means individual connections are put some separate lines.  You will never get the top speed of a bonded ADSL connection, and each line will have a different IP address, making hosting and resiliency nigh on impossible.

A Familiar Setup

A regular single line connection using ADSL involves an ADSL modem connected to a BT phone line.  Then, in order to share this connection across your network, you will have a router or firewall device that sits with one cable connecting it to the modem, and another to your network.

This kind of setup works for most single line connections and is a familiar setup.

A Bonded ADSL Setup

Increasing the number of lines and then bonding them together involves installing more than 1 BT phone line with broadband on it and then installing an additional device to do the actual bonding work on site.

So, like the single line setup, you have a series of modems all connected to their respective lines, but then instead of having a firewall on each, or all connected into the same firewall on different ports, with different IPs, they all get connected to a bonder.  Like a load balancer, but much better, this device, coupled with a carrier grade ISP server, does all the work for you, so that your network doesn’t know its dealing with more than one line.

The bonder then behaves like your “default gateway”, which used to be the ADSL modem.  Your firewall gets an IP address, or a block of them, sends all its internet requests to the bonder, through one single ethernet cable.

What Happens When A Line Goes Down?

Both the bonder on site, and the central bonder at the ISP constantly monitor the lines with tiny packets of data.  When they detect a problem, such as a line stopping responding, they stop the traffic flow on that line.

But the traffic remains flowing along the other bonded lines, and you won’t notice!

Of course, you need an ISP that cares when lines go down, and that take the headache away from you of dealing with BT for broadband faults, and whether lines need reporting or replacing.

With constant monitoring, you are informed when you need to be.  Some problems can be fixed without the customer even knowing about them, and others are often legitimately problems the customer has on site with their equipment.

Power outages are a very common issue, and you want an ISP that cares enough to call you if they see your connection is down, just to make sure everything is ok.

How Does IP Addressing Work With Bonded ADSL?

With a proper bonded ADSL connection, you can have a lot of flexibility with IPs, so you can tailor the connection to your business requirements.  Fully routed IPs, NAT IPs, private IPs, and any combination of them are available.

For example, you have  a VPN, so you need a fully routed IP on your firewall, but you also have a WiFi network that you don’t want to infringe the security of your LAN, but you do want to share your internet connection with.  It’s no trouble to have that fully routed IP, but also have a private range for your WiFi router, and have them both connected to the bonder sharing the same bonded ADSL connectivity.

Or you may just have a normal server setup for your small business, where you have a mail server, maybe an intranet or other web facilities for your staff.  You might have an FTP server, or Citrix or Remote Desktop services.  For this, a public routed NAT IP is perfect.  You can forward all of this traffic to its different servers through your firewall, but have the most efficient setup possible, by using only a single IP address.  With the growing shortage of IPv4 addresses, you are doing your bit for internet efficiency!