Chapter 6. First Hop Redundancy

Specifying a default gateway leads to a single point of failure. Proxy Address Resolution Protocol (ARP) is one method for hosts to dynamically discover gateways, but it has issues in a highly available environment. With Proxy ARP:

• Hosts ARP for all destinations, even remote.

• Router responds with its MAC.

• Problem: Slow failover because ARP entries take minutes to timeout.

Instead of making the host responsible for choosing a new gateway, router redundancy protocols enable two or more routers to support a shared MAC address. If the primary router is lost, the backup router assumes control of traffic forwarded to that MAC. This section refers to routers but includes those multilayer switches that ...

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