Trunk or Tagged Port

[Robert Peirce]

I am wondering if anyone can clarify an instance when I tagged port would used as opposed to a Trunk (port aggregation)?

It is my understanding that tagged ports are for interconectivty b/t two 802.1Q compliant switches. I am not sure if a trunk could also be used in this same instance.

Any clarification provided will be greatly appreciated.

[Ben Dehner · Accepted solution]

Tagging and trunks are really two different animals.

A trunk is a link aggregation of some type using two or more physical interfaces to create a logical interface for increased performance and fault tolerance. Trunk groups can be used between switches or from switches to hosts. There are several proprietary protocols for interswitch trunking, varying from vendor to vendor. The standard protocol is now is IEEE 802.3ad, otherwise known as LACP -- Link Aggregation Control Protocol.

Tagging is whether or not to add an 802.1Q header on to an ethernet packet. The 802.1Q header is used for two purposes, VLAN and 802.1p prioritization. Tagging is used almost exclusively between switches. You would use tagging if you were in an environment using VLANs or VoIP that required prioritization.

If you required increased bandwidth between switches, you could create a trunk group. (Assuming the switches supported a common protocol.) If the switches needed to pass tagged packets before, they will still need to pass tagged packets over the trunk group. Setting up a trunk group does not alter or elimiate the requirement for passing tagged packets.

However, setting up a trunk group can alter the configuration of packet tagging. Depending on the switch vendor, model, and protocol, some may require setting tagging on each port, while others may just require it on the trunk group as a whole.

[Robert Peirce]

Thank you providing such a concise and clear explanation.

Your response is greatly appreciated.

[Robert Peirce]

thank you for your response