Information Technology Reference
In-Depth Information
Figure23-15Pruning VLANs Already Reduces the Number of Blocked Ports and Avoids Unnecessary
Flooding
Trunk (1, 2, 3)
Core B
Core A
VLAN 2
VLAN 3
VLAN 3
VLAN 2
Dist2
Dist3
Users in VLAN 3
Users in VLAN 2
In this design, we have only one port blocked per VLAN. Note also that with this design, it is possible
to remove all redundant links in just one step by shutting down Core A or Core B.
Use Layer 3 Switching
Layer 3 switching means approximately routing at the speed of switching. A router performs two main
functions:
1.
It builds a forwarding table, generally exchanging information with its peers by the way of routing
protocols.
2.
It receives packets and forwards them to the correct interface based on their destination address.
High-end Cisco Layer 3 switches now can perform this second function, at the same speed as Layer 2
switching function. There is no speed penalty in introducing a routing hop and creating an additional
segmentation of the network. Figure 23-16 illustrates this, using the same diagram structure.
