Bridging And Routing Models; Traditional Bridging And Routing - 3Com CoreBuilder 2500 User Manual

3-4 C 3: B
HAPTER RIDGING AND
Bridging and
Routing Models
Traditional Bridging
and Routing
R C
OUTING IN THE ORE
The CoreBuilder 2500 system implements routing differently from the
way bridging and routing usually coexist. Traditionally, network systems
first try to route packets that belong to recognized protocols; all other
packets are bridged. In the CoreBuilder 2500 model, the system first tries
to bridge a packet. Then, if a packet's destination network address is not
on the same subnetwork, the system routes the packet.
The next sections describe these approaches.
In traditional routing, the bridge or router determines what to do with a
packet based on the packet's protocol. If the packet belongs to a
recognized protocol, the packet is routed. Otherwise, the packet is
bridged. Figure 3-4 illustrates traditional bridging:
1 The packet enters the bridge or router.
2 The bridge or router determines that the packet does not belong to a
recognized routing protocol, so the packet is passed to the bridge.
3 The bridge examines the destination MAC address and forwards the
packet to the port where that address was learned.
Router
2
1
Transmitting host
Figure 3-4 Traditional Bridging
B 2500 S
UILDER YSTEM
Bridge
3
Router vs. Bridge ?
Interfaces (ports)
Networks
Destination host