VLAN tagging

[hashaari]

Have a questioning concerning frame tagging for ethernet frame either using dot1q or ISL. In a cisco switch, where exactly does tagging occur? Is it at an access port or a trunk port? Apreciate your answer. Thanks.

[jolmo]

As far as I know, in both encapsulations, tag is added before sending the frame over the trunk link and removed at the receiving end.

HTH

[milan.kulik]

Correct.

Just note there is a native VLAN on Cisco 802.1q trunk which is sent untagged.

See http://www.cisco.com/cgi-bin/Support/browse/psp_view.pl?p=Technologies:Trunking&viewall=true

for many trunking articles.

Rgeards,

Milan

[amitsin]

Hi,

When we are talking about the trunk encapsulation the tagging occurs when the frame gets to the trunk port. In dot1q it internally tags the farme and in ISL it externally tags the frame and the tag gets rip off, the moment it hits the trunk port on the other side, When we talk about the access port tag the switch adds the PVID (Port Vlan ID Tag) on the frame the moment it hits the port and then the switch ports it to the other ports.

Hope this helps.

Amit Singh

[naorelkayam]

I think that in both ISL an DOT1Q the tag is added when is sent thrue the TRUNKed port and the switch on the other side removes the tag when it gets it... the difference is that DOT1Q dont tag the native VLAN and ISL does...

Maybe the image linked will help...

http://www.startimes.com.cn/html/jiejue/image/Image6-31.gif

Hope I helped...