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Implementing Cisco Networking Solutions by Harpreet Singh

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Virtual LANs

An Ethernet switch has multiple ports, and not all of them might be required for a LAN segment. As an example, consider that we have a 24-port switch model and we need to create two different LAN segments with 10 hosts in one segment and 12 in the other. Virtual LAN technology allows a switch to be partitioned into multiple virtual switches or Ethernet segments. The MAC table in a switch that allows VLANs has additional information in addition to the one seen earlier. Each VLAN is denoted by a number, and there can be 4094 theoretical VLANs using 12 bits. There are some reserved VLAN numbers for FDDI and token ring, and not all switches will support 4094 VLANs.

The following figure shows a physical switch with 24 ports numbered ...

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