3Com LANPLEX 2500, User Manual

Page: 40 / 186

3-6 C
HAPTER
3: B
RIDGING AND
R
OUTING IN THE
LAN
PLEX
® S
YSTEM
LANplex Bridging
and Routing Model
The LANplex 2500 system uses the destination MAC address to
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):
1 The packet enters the LANplex system.
2 The packet’s destination MAC address is examined by the bridging layer.
3 The 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.
Figure 3-6 Bridging in the LANplex Bridging and Routing Model
1
Transmitting Host
3
Destination Host
2
1
2
3
Router Interfaces
Bridging Layer
Routing Layer
Subnets
1 2 3
Router
Bridge