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I am relatively new to networking; I love to learn, but like to firmly grasp a concept before I move on. This being said, I researched what a trunk port is and I found this definition:

[It transmits] data from multiple local area networks (LANs) or virtual LANs (VLANs) across a single interconnect between switches or routers.

My question is, why can't I just connect two switches to one another without configuring a trunk port? What is the difference between a standard port and a trunk port? Perhaps I just don't understand it very well. Help would be very much appreciated!

Jordan
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To undestand that, it is important to understand the concept of VLANs.

Typically there is often a tagged VOIP VLAN and and a untagged Network VLAN on Office LAN connections. The wireing is through the phone ports just needing a single cable for two different LANs. The PC is then connected to the phone.

On the switch side a trunk port is often configured carring multiple tagged VLANs. There are many situations where this is used and helpful when dealing with complex networks.

Still technically you can also configure trunk ports to only carry a untagged network. Further many switches do allow configuration of standard ports to carry multiple tagged VLANs. Often switch trunk ports also have special characteristics like not filtering on layer2 mac addresses, which is typically not possible on standard ports. Or beeing able to configure the trunk ports for port mirroring.

hargut
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  • @harhut Ohhh gotcha. I did some research just now on tagged vs untagged VLANs and it is making a little more sense. // However, I noticed that you said that a trunk port is often configured for carrying multiple *tagged* VLANs. Does this mean that if you have 2 VLANs (one being tagged and the other not) you don't necessarily need a trunk port? // So in essence, configuring a trunk port allows you to have more functionality and control of your VLANs? Thank you for your help, by the way. – Jordan Jul 24 '18 at 22:00
  • A VLAN always has a VLANID/tag. On an access port you can "remove" that tag, and make a tagged VLAN untagged. The connected client then has no need to deal with VLANs. – hargut Jul 25 '18 at 05:41
  • With that in mind, there is no untagged VLAN on a trunk port. Say 2 VLANs one with ID/Tag 10 second with 20. Inside the switch these are always tagged, but you can configure access ports to have 20 untagged, or 10 untagged. When using a trunk port to expand these VLANs to other switches there will only be tagged VLAN 10&20. – hargut Jul 25 '18 at 05:48
  • in dummy terms (for me) then, tagging is what identifies traffic as part of x VLAN? And all VLAN's need to be tagged when going through a trunk port because otherwise the traffic might get mixed up? – Jordan Jul 25 '18 at 19:12