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Cisco LAN Switching Fundamentals by Basir Sakandar - CCIE No. 6040, David Barnes - CCIE No. 6563

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VLAN Pruning

One of the major problems with extending Layer 2 architecture is excessive unwanted traffic on the network. A pruning method can be implemented on Cisco switches to prune VLANs from going to switches that do not have any hosts for that VLAN. It is important to note that although pruning can prevent some unnecessary traffic from being circulated across the network, pruning VLANs does not simplify the spanning-tree topologies.

By default, a trunk port allows all VLANs through the trunk as shown in Example 4-8. Trunk 10/27 goes from Switch1 to Switch4.

Example 4-8. Output of show trunk Command Connected to Switch4
Switch1 (enable) show trunk 10/27 * - indicates vtp domain mismatch Port Mode Encapsulation Status Native vlan -------- ...

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