Having seen and done a lot with Windows Network Load Balancing(NLB), I thought it might be helpful for those who aren't familiar with NLB if I wrote a series of posts which explain what it is and how it works - from the beginning.  To start the journey, this post will explain, at a basic level, how it works and why it is different to other solutions.  Future posts will explore more detail on how it works and various ways you might use it for your hosting solution.

So what is it?

Simply put, it is an algorithm that a group of servers use to determine which server will process inbound network traffic at a point in time.  English?  Well, perhaps I'll explain what it is not first.

You may be forgiven for thinking it works similarly to a hardware load balancer - a device that logically sits in front of the servers you are hosting, and then directs each incoming request to a server according to rules set on the device.  The hardware load balancer will ensure that the traffic load is distributed across the servers.  Or to put it another way, it is a traffic cop that directs each network packet to a particular server so that each server is receiving an equal number of requests.  This is an overly simple explanation for illustration only.

NLB does not do this - it uses a different strategy to achieve the same goal.  When you use NLB, every packet is delivered to every server.  What NLB then does is use an algorithm to decide which server will process a particular packet, and the rest of the servers will drop the request and not process it. 

So, in summary, a hardware load balancer directs individual packets to a certain server in a set of servers, whereas NLB works by all servers receiving all packets with only one server processing the packet. 

How does NLB achieve this?  Well, this will be the focus of the next blog entry on this topic.

Happy hosting.

Ben