While comparing broadband packages from Tata Indicom and BSNL Dataone, I came across the revised pricing of another provider with whom I have a love-hate relationship. My last experience with them was ok.

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In many location, including but definitely not limited to India, single ADSL / Cable connections can be unreliable and also may not provide sufficient bandwidth for your purposes. One way to increase reliability and bandwidth of your internet connection is to distribute the load (load balancing) using multiple connections. It is also imperative to have transparent fail-over so routes are automatically adjusted depending on the availability of the connections. With load balancing and fail-over you can have reliable connectivity over two or more unreliable broadband connections (like BSNL or Tata Indicom in India). I present you with the simplest solution to a complex problem with live examples.

Note: Load balancing doesn't increase connection speed for a single connection. Its benefits are realized over multiple connections like in an office environment. The benefits of fail-over are however realized even in a single user environment.

The load balancing mechanism, to be discussed with example below, in Linux caches routes and doesn't provide transparent fail-over support. There are two solutions to incorporate transparent fail over - 1. compiling and using a custom Linux kernel with Julian Anastasov's kernel patches for dead gateway detection or 2. user space script to monitor connections and dynamically change routing information.

Julian Anastasov's patches have two problems:
1. They work only when the first hop gateway is down. In many cases, including ours, the first hop gateway is the adsl modem cum router which is always up. So we need a more robust solution for our purposes.

2. You have to compile a custom kernel with patches. This is somewhat complex procedure with reasonable chances of screwing up something. It also forces you to re-patch the kernel every time you decide to update your kernel. Overall I wouldn't recommend anyone going for kernel patching route unless that is the only option. Also in that case you should look for a rpm based solution (like livna rpm for nVidia drivers) which does it automatically for you.

A better solution is to use a userspace program which monitors your connection and updates routes as necessary. I will provide a script which we use to constantly monitor our connections. It provides transparent fail over support with two ADSL connections. It is fully configurable and can be used for any standard dual ADSL / Cable connections to provide transparent fail over support. It can also be easily modified to use for more than two connections. You can also use it to log uptime / downtime of your connections like we did.
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eBox platform provides a mini-debian installation along with its modules to allow you to provide and manage network services on your corporate network. The key capabilities includes support for multiple external network interfaces with load balancing, traffic shaping, transparent proxy, firewall, content filters, DNS (domain name server), NTP (time server), mail server, Jabber Instant Messaging server, SAMBA for file sharing, DHCP and more. In short it promise to be a one-stop solution for all network services needs for small businesses. Particularly I was interested in load balancing between multiple ADSL providers and traffic shaping capabilities. Here are my experiences with eBox platform.

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