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Knowledge base Bonding lines

There are many ways to bond multiple lines together and there are different reasons for wanting to do this. The main reasons are extra overall speed, and added redundancy against failure.

Our broadband services allow use of multiple lines to provide both of these objectives.

One of the key benefits of our service is that downlink bonding can be achieved with nothing more than multiple cheap ADSL routers on your network. There is no need for expensive multi-line ADSL routers.


Our Home::1 and SoHo::1 packages allow you to have a quota on each line but multiple lines at the same site balance so you can have the total quota used over all lines as you wish. Our Office::1 package is multiple lines as standard.

This means you can mix and match quotas at any level on ADSL and/or VDSL lines at the same site. You will need the lowest quota at least on each line, but you can mix a 2TB on one line and 200G on another line to have a 2.2TB total Home::1 for example.

Note: Our old units based package allow units over a whole site and charge an extra line rate for additional lines.

Fast failover

It is important that when a line fails for any reason the service switches automatically to using the remaining lines. Our constant quality monitoring system means we are constantly monitoring every line and will be able to react to a failure of a line within 10 seconds. When a line goes out of service the routing of traffic can automatically switch to remaining lines.

When using multiple lines for redundancy this allows the fall-back line to come in to service very quickly. When being used for extra speed the failed line simple means less speed until the problem is resolved.

We provide email and text alerts of lines going off line unexpectedly so that you are alerted to the problem.

Faster speed (download)

To achieve a faster overall speed traffic sent from the internet to you can be sent using multiple lines. This is done by sending each packet down one of the lines in a load balanced way so that overall the traffic is balanced between the lines. The speed of the lines is taken in to account so that a slower line will be sent less traffic than a faster line. The packets then arrive at your routers at your end and arrive on your LAN.

The effect of this is that the two or more lines are used at once, so even a single file transfer will be able to make use of all of the lines.

The only downside of this method is that sometimes packets can arrive in a slight different order to which they were sent. This is normal and part of the IP protocol. However, not all systems handle out of order packets as well as they could so the more lines you have the less effective the bonding is.

This means there is no overhead for bonding, but if you have lines with very different latency or lots of lines the packet ordering can mean diminishing returns for more lines. Two lines generally works very well though.

Faster speed (upload)

Like most ISPs we restrict what traffic can be sent to us so that it must be from one of your IP addresses. However, unlike most ISPs we are able to set up your IP addresses over your multiple lines. This allows you to send us traffic from any of your IP addresses via any of the lines on your site.

What this means is that you can do with uplink what we do with downlink - you can send packets up any of the lines and load balance them to achieve a higher uplink speed overall.

What this does mean is that you have to have equipment to do this.


A FireBrick can provide monitoring of your lines and routing of traffic up multiple lines. The FireBrick FB2900 (fully loaded) can handle total speeds up to 750Mb/s.


A linux router can provide routing on per packet or per session for traffic to use multiple lines. You may need to make scripts to monitor lines to arrange for fall-back. We hope to have a more detailed knowledge base article on this soon - in the mean time we suggest you ask other customers on irc or usenet.

Simple fall-back

Most ADSL routers allow manual routes to be configured. This means you could configure an ADSL router to use a second router as its default route when its broadband link is down. Doing this means you can use one of your routers as a gateway, and it can automatically fall-back to the other if the line fails.

IP addressing and routing

Our control pages allow you to adjust the IP routing on your lines. You can have multiple IP addresses on a login, and each can be set for routing to one or more lines. You can set each IP address block separately and can define backup routing.

The recommended set up is to use a FireBrick and multiple PPPoE modems or bridges. The FireBrick would have one WAN address over all of the lines, and either public Legacy IPv4 addresses on the LAN, or private address and NAT on the FireBrick. In either case you can have public IPv6 addresses on the LAN and still handle bonding down and up on multiple lines.

The alternative if to use separate routers. These would normally share a /29 interlink subnet and connect to some firewall or router within you network, routing a static IP block to that router. The interlink address block could be private IPv4 addresses but you do not want NAT or fire-walling on the external routers even in that case as it will not handle the bonding. In general using the FireBrick and PPPoE is simpler and more flexible.

Tunnelled bonding

Another approach is to use a tunnelling system of some sort such as a VPN or FireBrick tunnels to tunnel traffic via one or more lines to a tunnel endpoint held in a data centre. We offer hosting services and host FireBricks as tunnel endpoints. Using FB2900's at both sides will allow multiple tunnelled connections which can be via multiple ADSL lines that are even from different internet providers.