FHRP Concepts
When networks use a design that includes redundant routers, switches, LAN links, and WAN links, in some cases other protocols are required to both take advantage of that redundancy and to prevent problems caused by it. For instance, imagine a WAN with many remote branch offices. If each remote branch has two WAN links connecting it to the rest of the network, those routers can use an IP routing protocol to pick the best routes. When one WAN link fails, the routing protocol can learn routes that all happen to use the one remaining WAN link, taking advantage of the redundant link.
As another example, consider a LAN with redundant links and switches, as discussed in Chapters 1, “Spanning Tree Protocol Concepts,” and 2, “Spanning Tree ...
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