3Com 2500 manual Bridging in the LANplex Bridging and Routing Model

3-6 CHAPTER 3: BRIDGING AND ROUTING IN THE LANPLEX® SYSTEM

LANplex Bridging The LANplex 2500 system uses the destination MAC address to

and Routing Model determine whether it will bridge or route a packet. Before a host system sends a packet to another host, it compares its own network address to the network address of the other host as follows:

■If network addresses are on the same subnet, the packet is bridged directly to the destination host’s address.

■If network addresses are on different subnets, the packet must be routed from one subnet to the other. In this case, the host transmits the packet to the connecting router’s MAC address.

In the LANplex bridging/routing model, a packet is bridged as follows (see Figure 3-6):

1The packet enters the LANplex system.

2The packet’s destination MAC address is examined by the bridging layer.

3The destination MAC address does not correspond to the MAC address of one of the system ports configured for routing. The bridging layer selects a segment (port) based on the destination MAC address and forwards the packet to that segment.

		Router
			Routing Layer
1	2	3	Router Interfaces
3		Bridge
2			Bridging Layer
1
1	2	3	Subnets

Transmitting Host

Destination Host

Figure 3-6 Bridging in the LANplex Bridging and Routing Model