Layer 3 Switching

Layer 3 Switching
The only difference between a layer 3 switch and a router is the way the administrator creates
the physical implementation. Also, traditional routers use microprocessors to make forwarding
decisions, and the switch performs only hardware-based packet switching. However,
some traditional routers can have other hardware functions as well in some of the higher end
models. Layer 3 switches can be placed anywhere in the network because they handle highperformance
LAN traffic and can cost-effectively replace routers.
Layer 3 switching is all hardware-based packet forwarding, and all packet forwarding is
handled by hardware ASICs. Layer 3 switches really are no different functionally from a traditional
router and perform the same functions, which are listed here:
 Determine paths based on logical addressing
 Run layer 3 checksums (on header only)
 Use time to live (TTL)
 Process and respond to any option information
 Can update Simple Network Management Protocol (SNMP) managers with Management
Information Base (MIB) information
 Provide security
Using Switching Technologies 393
The benefits of layer 3 switching include the following:
 Hardware-based packet forwarding
 High-performance packet switching
 High-speed scalability
 Low latency
 Lower per-port cost
 Flow accounting
 Security
 Quality of service (QoS)