VLAN Tagging - Explanation please

[cre8toruk]

Hi all,

I'd preface this with an apology if this is a dumb question. I am an enthusiastic amateur so I may not get all the terms correct.

Could you please explain to me what VLAN tagging is and why I need to use it?

I think I understand correctly that a packet coming from a switch port that is configured with an access port in VLAN 10 (for example) is tagged automatically with a VLAN tag of 10.
I think I also understand correctly that when the same packet hits a trunk port it is transported to wherever it needs to get to (sort of)… So my question is I guess, what's the difference between a tagged and an untagged packet and when would I use a tagged packet over an untagged one?

thanks in advance.

Paul.

[balaji.bandi]

here is the good document to understand better :

http://www.firewall.cx/networking-topics/vlan-networks/219-vlan-tagging.html

[Reza Sharifi]

Hi,

Have a look at this document

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus5000/sw/configuration/guide/cli/CLIConfigurationGuide/AccessTrunk.html

HTH

[Joseph W. Doherty]

"I think I understand correctly that a packet coming from a switch port that is configured with an access port in VLAN 10 (for example) is tagged automatically with a VLAN tag of 10."

Generally incorrect (if we're discussing a VLAN Ethernet frame tag).

Trunk ports is where you normally see tagged frames.

The reason is simple. On an usual access port, the port is assigned to one VLAN and frames entering it, or leaving it, are untagged. (Also generally, the hosts on access ports are VLAN blind, i.e. they exspect all their frames to be untagged.)

(Cisco) Trunk ports are used to carry multiple VLANs between different (usually) switches. So that the two network devices can tell which frames belong to which VLANs, tags are added to the frame.

Be aware the foregoing is the very simple version.