Tagging and Untagging Questions

[Tom Hardy]

Hello,

Can someone please tell me how tagging and untagging works? I thought i knew how it works but after reading some threads on here, i confused me.

Thanks for all replies in advance.

[Jeff Carrell · Accepted solution]

this is all based on the IEEE 802.1Q standard...

basic rules:

1) a port can be untagged in at most 1 vlan at a time

2) a port can be tagged in as many vlans as are in the switch config

an untagged port is what you normally connect an endpoint device (computer, printer, server, camera, badege reader, sometimes a VoIP phone, etc)...

a tagged port is used "mostly" to interconnect switches that carry multiple vlans on that link...

a tagged frame has an extra 4 bytes in the middle, which has the vlan id, qos settings, and a few other bits of data...

"normal" endpoint devices are not configured to speak tagged...altho there can be exceptions to this rule given very specific configuration/operation requirements (servers, VoIP phones, AP's)...but generally a user computer speaks untagged...

hth...jeff

[Tom Hardy]

Thanks for all your help :)

So lets say i have two vlans.

vlan1 (Data)
vlan2 (Voice)

And i want both voice and data vlans to go out of the same port (voip phone and pc daisy chained), i need to set that port to untagged? But you said that i can only have one vlan on an untagged port.

im confued :(

[Jeff Carrell]

ah, here's one of those exception times :-)

in order to have these 2 kinds of traffic into a single port, you set the port to untagged in the data vlan, and tagged in the voice vlan...

you then have to configure your phone to speak tagged...

the phone traffic will then get where it needs to be in the voice vlan, and the data coming thru the phone will get into the data vlan where it needs to be...

cheers...jeff

[Tom Hardy]

Got it. Seriously, thanks for all your help :) I really appreciatte the time you took to answer my questions.

[Tom Hardy]

Question Answered