What is a Switchport Trunk Allowed VLAN?

A switchport trunk allowed VLAN is a feature in networking that allows multiple VLANs to be carried over a single physical link between two network devices. This is achieved by configuring the switchport as a trunk port and specifying which VLANs are allowed to pass through the link.

How Does Switchport Trunk Allowed VLAN Work?

When a switchport is configured as a trunk port, it is able to carry traffic for multiple VLANs. By default, all VLANs are allowed to pass through the trunk port. However, this can be a security risk as it allows all VLANs to communicate with each other. To mitigate this risk, network administrators can specify which VLANs are allowed to pass through the trunk port.

For example, if a network has three VLANs (VLAN 10, VLAN 20, and VLAN 30), and a switch needs to communicate with another switch on the network, the switchport connecting the two switches can be configured as a trunk port. The network administrator can then specify that only VLAN 10 and VLAN 20 are allowed to pass through the trunk port. This means that VLAN 30 traffic will not be able to pass through the link, providing an additional layer of security.

Benefits of Switchport Trunk Allowed VLAN

Switchport trunk allowed VLAN provides several benefits to network administrators, including:

• Increased network security by limiting which VLANs can communicate with each other
• Reduced network congestion by allowing multiple VLANs to share a single physical link
• Improved network performance by separating traffic into different VLANs
• Greater flexibility in network design by allowing VLANs to be easily added or removed from the trunk port

Conclusion

Switchport trunk allowed VLAN is a powerful feature in networking that allows multiple VLANs to be carried over a single physical link. By configuring the switchport as a trunk port and specifying which VLANs are allowed to pass through the link, network administrators can improve network security, reduce congestion, improve performance, and increase flexibility in network design.

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