O'Reilly logo

CCNP Quick Reference Sheets Bundle: Exams 642-901, 642-812, 642-845, 642-825 by Jay Swan, Denise Donohue, Brent Stewart

Stay ahead with the world's most comprehensive technology and business learning platform.

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

Start Free Trial

No credit card required

Chapter 5. Layer 3 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, Layer 3 redundancy protocols allow 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 Layer 3 switches that can also implement Layer ...

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

Start Free Trial

No credit card required