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Chapter 1
The Campus Network
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
high-performance 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 dif-
ferent functionally than 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 responds to any option information
Can update Simple Network Management Protocol (SNMP) manag-
ers with Management Information Base (MIB) information
Provide Security
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)
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