Tagged vs Untagged on HP switches

[Possey]

Hi,

i'm new to the VLAN scene and on my new job I need to manage the network. 

I've already read about tagged and untagged ports and I just had a couple more questions to check if I got it all right.

On my network I can see that there is a connection between 2 switches. Both switches have untagged ports belonging to VLAN 1 or VLAN 2. The ports that are connecting the two switches have the following configuration: 

vlan 1 untagged and vlan 2 tagged. I wonder why this is. If traffic should go from switch to switch, then I would think that the port should be vlan 1 tagged and vlan 2 tagged. Or does this not make any difference?

Other general questions are:

if an untagged port receives tagged packets (with same VLAN ID of the untagged port), will it drop the packet or will it just remove the tag from the packet ?

if an untagged port receives tagged packets (with different VLAN ID of the untagged port), will it drop the packet or will it just remove the tag from the packet ?

if an tagged port receives untagged packets, willl it drop the packet?

Thanks in advance.

[TamNP]

Hello Possey,

Please refer to this thread
http://h30499.www3.hp.com/t5/Switches-Hubs-Modems-Legacy-ITRC/Tagged-vs-Untagged/td-p/4004330#.U5fWWyjLP74

[Possey]

Hi,

Thanks for the reply.

I still don't understand completely.

So the link between the 2 switches may be set to untagged because it only carries frames from VLAN 1.

But may it the ports also be set to Tagged vlan 1 ? Does that make a difference ?

Could you also answer my other questions ?

if an untagged port receives tagged packets (with same VLAN ID of the untagged port), will it drop the packet or will it just remove the tag from the packet ?   

if an untagged port receives tagged packets (with different VLAN ID of the untagged port), will it drop the packet or will it just remove the tag from the packet ?

if an tagged port receives untagged packets, willl it drop the packet?

Thanks in advance

[AtticaNet]

Hello,

For a quick reply.
The tagging and untagging is just so the switch can send the information to the proper port.

As you mentioned the ports need to be assigned to a VLAN.

The switch will deliver the information to those ports that are members of the same VLAN.

So a port member of VLAN 1 can only receive information from other ports also in VLAN 1.

When you connect two switches, which have multiple VLANs, the switch needs to be able to determine which information goes to which port. Thus you tag and untag VLANs not ports.

The switch will read the VLAN tag and route the information to the ports part of that same VLAN. Before the switch delivers the message it removes the VLAN tag from the frame.

Regards.