Two or more routers grouped together to provide any combination of hardware redundancy, service redundancy, load balancing and increased speed. The speed enhancement is accomplished by bonding the routers together. For example, three separate routers such as T1, T3, E1, E3 or wireless, can be combined to provide three times the speed, reliability and redundancy. Although failover can be accomplished in routers through software, all of the features mentioned either require additional hardware within the router or an external router cluster device.
In this diagram, two FatPipe Xtreme router cluster units connect three routers and provide automatic failover if any unit ceases to function or if the connection to one of the ISPs fails. Each Xtreme unit can connect to the LAN and three routers, which can be of a mixed variety. (Diagram courtesy of FatPipe Networks, www.fatpipeinc.com)