3Com CoreBuilder 3500, Implementation Manual, Page: 278 / 592

278 C
HAPTER
11: I
NTERNET
P
ROTOCOL
(IP)
In Figure 51, a Layer 2 switch is acting as a port aggregator for the
corporate or campus VLAN. Because the traffic going from the Layer 2
switch to the Layer2/Layer 3 switch is only going to be routed, port-based
routing between these two devices is more efficient.
Figure 51 Port-based Routing (Port Aggregation)
Benefits of Port-based Routing
Because the bridge and router topologies are different, Spanning Tree
Protocol (STP) can build a spanning tree that is not associated with the
routing topology.
This is especially useful if you want to configure two routers in parallel
and let the routing protocol or protocols manage the routing loop while
STP simultaneously manages any potential bridge loop. This redundant
router configuration is widely used to incorporate:
■
Network redundancy.
■
Load sharing between two routers on the same two LANs.
Limitations of Port-based Routing
The system can only supply to the interface the physical bandwidth limit
of the port, since the interface is strictly associated with one physical port.
L3
3.3.1.254/255.255.255.0
Port-based Router Interface
3.3.1.0 Subnetwork
L2
End Hosts