Because I have a dream... I dream of a world where people stop calling a link balancer a load balancer - because we don't sell link balancers!
And I'm sure that the team at Mushroom Networks have the same dream - because they don't sell load balancers!
What is load balancing?
Load balancing is a way to distribute traffic coming from the internet to a server. It works by having a Virtual IP (VIP) in front of real servers with IP's (RIPs). The load balancer would be the VIP and behind the VIP would be a series of real servers.
The VIP would then choose which RIP to send the traffic to depending on different variables, such as server load and if the real server is up etc. The reason for a load balancer is that the traffic will be shared between servers - this will therefore mean that one server will not get overwhelmed with traffic and break due to the amount of traffic hitting it from the internet.
A typical use case for a load balancer is to ensure availability, performance and maintainability of a server based application.
Check out this network diagram for a typical load balanced deployment:
OK...so what's link balancing then?
Link balancing, on the other hand, is a completely different beast!
Link balancing is designed to balance the load between the local area network (LAN) and the Internet. A link balancer is usually positioned between the LAN and the WAN (wide area network).
The link balancer uses traffic management algorithms in order to make sure that each link is being used to the best of its ability. Potentially, it can work out the fastest route for the information, by taking into account which ISP link has the most bandwidth available before it chooses the best path.
A typical use case would be to combine multiple Internet links to increase the agregate available bandwidth, performance and redundancy. The link balancer would balance the traffic by using algorithms on which router an ISP has the most available bandwidth and send the traffic in that direction.
Below is a diagram of a link balancer. The diagram shows how the users in the LAN's request go through the link balancer, which chooses the best router and ISP in order to connect the user to the internet.
Basically, link balancers and load balancers do similar jobs. They calculate the best place to send the user to, which helps increase efficiency and speed without crashing the server or router.
So, in short (and probably the best way to remember the difference) - load balancers control traffic from the internet and distribute that traffic to the best available server. Link balancing distributes requests from the LAN across multiple Internet links and guides traffic to the best available destination.