If you run most any type of services in a production environment, chances are, you want some sort of redundancy and load balancing. As an example, if you're running a web site, you want that to be up as much as possible, so generally a load balancer is used to send the load between different web servers. A common load balancer used is a big-ip F5. These have a great configuration tool and work very well, but they're also very expensive.

Here's the OSI Model in networking:

1. Application layer
2. Presentation layer
3. Session layer
4. Transport layer
5. Network layer
6. Data Link layer
7. Physical layer

Here's how I remember it:

1. A
2. Priest
3. Saw
4. Ten
5. Nuns
6. Doing
7. Pushups

I seem to remember it because it seems like it should be a dirty joke, even though it isn't.