3-4 CHAPTER 3: ROUTING AND THE LANPLEX SYSTEM
Ethernet ports to expand your existing subnets. This is in contrast to
more traditional forms of bridging and routing where, at most, one port
is connected to any subnet.
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/Routing Models
The way routing is implemented in the LANplex system differs from
how bridging and routing usually coexist in a system.
■Traditional Bridging/Routing Model — In this model, 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/Routing Model — In this model, the bridge and
router operate hierarchically on the module — routing over bridging.
When a packet enters the system, the module first tries to bridge the
packet. If the packet’s destination network address is not on the same
subnet, then the module routes the packet.
Traditional
Bridging/Routing
Model
The bridge/router determines whether a packet should be bridged or
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/routing model, a packet is bridged as follows
(see Figure 3-4):
1The packet enters the bridge/router.
2The bridge/router determines that the packet does not belong to a
recognized routed 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.