Points of Failure
TechWeb’s TechEncyclopedia defines redundancy as “...peripherals, computer systems and network devices that take on the processing or transmission load when other units fail.” More granularly, redundancy is the inclusion of independent yet identical sets of components to provide an alternate way of providing a function. The concept of redundancy can be applied to individual computers, sets of computers, networks, and even entire implementation design. Moreover, systems can be as redundant as needed; as with everything, however, there is a “happy medium.”
I should discuss certain terminology in regard to redundancy before proceeding further. A technique to balance and distribute loads across servers working in tandem is called a “round robin” strategy. For example, let’s say I have three RADIUS servers in one POP. The NAS is configured to send calls in order to one of the three RADIUS servers; the mentality behind this is that the traffic load will be evenly placed among the three servers by choosing the next available server in the “list” upon dial-in so that no one server is operating under a much heavier load than the others.
Secondly, “failover” is a term used to describe when an administrator has ensured service availability by enabling a service to cut over to another standby server when a primary server fails. This is most commonly found in groups of two servers in one geographic location, such as a particular POP in a city. There may be two RADIUS servers, ...