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VTP for VLAN management
Mod Comms
Virtual LANs (VLANs) are used widely in modern network infrastructures. A VLAN can divide a physical LAN into small pieces of virtual LAN to contain broadcast traffic in a limited, reasonable range. In technical terms, it breaks the network into different broadcast domains.
All hosts in a switched network are required to listen and supply resources to process broadcast messages, even when they are not the target. Decreasing the frequency of broadcast messages by breaking the network into domains can avoid wasting host CPU power. Also, limiting the broadcast can prevent switches from wasting bandwidth to forward messages to unnecessary ports. Finally, because hosts in different VLANs cannot communicate with each other directly, VLAN can also provide security.
A host can be assigned to any VLAN regardless of geographic location, as long as the switches are connected by trunk links. VLANs need to be created on all switches on the path through which VLAN traffic passes. For example, in Figure 1 (see also Listing 1 for the configuration commands), VLAN20 needs to be created on SW1 and SW2 for red hosts to communicate, whereas VLAN 30 must be on SW2 and SW3 for the blue hosts to communicate. If you want the green hosts to communicate, all three switches would need VLAN10.
Listing 1
VLAN Configuration Commands
SW1(config)#vlan 10 SW1(config-vlan)#name Accounting_Dept SW1(config-vlan)#vlan 20 SW1(config-vlan)#name IT_Dept SW2(config)#vlan 10 SW2(config-vlan)#name Accounting_Dept SW2(config-vlan)#vlan 20 SW2(config-vlan)#name IT_Dept SW2(config-vlan)#vlan 30 SW2(config-vlan)#name Marketing_Dept SW3(config-vlan)#vlan 10 SW3(config-vlan)#name Accounting_Dept SW3(config-vlan)#vlan 30 SW3(config-vlan)#name
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