3Com 2500 manual Bridging and, Routing Models

3-4 CHAPTER 3: BRIDGING AND ROUTING IN THE LANPLEX® SYSTEM

	In the traditional model, if you want to increase the level of
	segmentation in your network, you must create additional subnets and
	assign new network addresses to your existing hosts.
Bridging and	The way routing is implemented in the LANplex system differs from
Routing Models	how bridging and routing usually coexist in a system.
	■ Traditional Bridging and Routing Model — Traditionally, bridging and
	routing are peer entities; either a packet is bridged or routed. Packets
	belonging to recognized protocols are routed; all others are bridged.
	■ LANplex Bridging and Routing Model — In the LANplex model, the
	bridge and router operate hierarchically on the LANplex system, routing
	over bridging. When a packet enters the system, the system first tries to
	bridge the packet. If the packet’s destination network address is not on
	the same subnet, then the system routes the packet.

Traditional Bridging The bridge or router determines whether a packet should be bridged or and Routing Model routed based on the protocol to which the packet belongs. If the packet

belongs to a recognized protocol, the packet is routed. Otherwise, it is bridged.

In the traditional bridging and routing model, a packet is bridged as follows (see Figure 3-4):

1The packet enters the bridge or router.

2The bridge or router determines that the packet does not belong to a recognized routing protocol, so the packet is passed to the bridge.

3The bridge examines the destination MAC address and forwards the packet to the port on which that address has been learned.