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Cisco LAN Switching Fundamentals by Basir Sakandar - CCIE No. 6040, David Barnes - CCIE No. 6563

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Understanding the Need for Cisco Express Forwarding

To appreciate the advantages offered by Cisco Express Forwarding (CEF), it is important to understand some of the shortfalls of flow-based switching mechanisms, such as MLS, described in the previous sections. MLS works well for the most part. After the first packet, all other packets are hardware switched. The switching of the packet at hardware provides higher performance many times over than software-based switching done by a router. The problem with MLS implementation is that the first packet always hits the router. Any network changes caused by neighbor resets, route flaps, and aging timers can cause the MLS table for those specific entries to get flushed. This puts unnecessary burden ...

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