Simply stated, Layer 3 switching is
hardware-based routing. In particular, the packet forwarding is
handled by specialized hardware ASICs. The goal is to capture the
speed of switching and the scalability of routing. A Layer 3 switch
acts on a packet in the same way that a traditional router does, for
example:
- Determining the forwarding path
based on Layer 3 information
- Validating the integrity of the
Layer 3 header via checksum
- Verifying packet expiration and
updates accordingly
- Processing and responding to any
option information
- Updating forwarding statistics in
the Management Information Base (MIB)
- Applying security controls if
required
- Implementing quality of service (QoS)
The primary difference between the
packet-switching operation of a router and a Layer 3 switch lies in
the physical implementation. In general-purpose routers,
microprocessor-based engines typically perform software-based packet
switching. A Layer 3 switch performs packet switching with hardware.
Because it is designed to handle high-performance LAN traffic, a
Layer 3 switch can be placed anywhere within the network, offering a
cost-effective alternative to the traditional router.
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