The traffic that the client initializes will get to the Load-Balancer that has the virtual load-balanced IP. However, the Load-Balancer is using only one interface and this interface is on the same L2 network with all the servers.
![router on a stick explained router on a stick explained](https://i.ytimg.com/vi/nmSvjGh_Hss/maxresdefault.jpg)
It is not important how far away the Client worksations are, they can be behind internet or in the same LAN and the load-balancing would be the same. So let’s have a look at the following topology with One-Arm solution to understand what the Load-Balancer has to do.
![router on a stick explained router on a stick explained](http://orbit-computer-solutions.com/wp-content/uploads/2015/10/troubleshooting-routeron-a-stick-intervlan.jpg)
One-Arm means that the Load-Balancer is not physically “in-line” of the traffic, but as you might understand right now, it has to get into the way of traffic somehow, to have control over all the Client to Server connections going in both ways. Return traffic is going back via the Load-Balancer and the source IP is again changed to the virtual load-balanced IP in the response to the Client. During this proces, the destination physical server is chosen by the load-balancing algorithm. As such, he can simply do destination IP NAT in client request coming to the load-balanced virtual IP and forward the packet to one of the servers in server farm. The picture is generalized for overview purposes and you can note the Load-Balancer separating users and server physically, therefore all the traffic has to go via the Load-Balancer.Īs you can agree, the Load-Balancer is also a router between the “Front End” and “Back End” networks. To be honest I didn’t yet seen an two-arm scenario deployed as switched mode in real production networks because there is no need for this most of the time and there are no big advantages against the Two-Arm in routed mode.īasic scenario of routed two-arm solution can be seen on next picture that. For the “transparend mode”, the same traffic paths would apply, but the load-balancer has to intercept traffic at L2 to load-balance by changing L2 frames to get them to the physical routers in server farm.īut let’s get back to the routed mode scenario as it is much simpler, cleaner, more easy to troubleshoot and therefore deployed much more often. But I will only focus on the routed mode as it is the most common and more easy to understand. The scenario diagram would be the same with the exception that the Load-Balancer would be essentially a switch load-balancing by modifying L2 frames. In general Two-Arm can also be used in something called “bridge mode” or “transparent mode”. Two-Arm is basic scenario where you have a server farm in one side of the network (Back End) and the load-balaner is essentially the default gateway router for the physical servers in the Back End network. This article is an introduction to the load-balancers three basic configuration scenarios to give you an overview before other articles start to explore load-balancing solutions in more detail. If you don’t, do not worry and just read on. Once you know the basic principles, every load-balancer from any vendor is very easy to configure once you you know the three basic scenarios that are mostly deployed in real life.
![router on a stick explained router on a stick explained](https://www.orbit-computer-solutions.com/wp-content/uploads/2015/10/troubleshooting-routeron-a-stick-intervlan-250x207.jpg)
Load-Balancing is in principle a wonderful thing really.