VLAN Tagging

Unanswered Question
Jul 7th, 2010

Hi,

Need a quick refresher....

How do cisco switches tag intra-vlan traffic within the chassis?

So, an ethernet packet on an access port in vlan 10 needs to get switched to another acces port on vlan 10 (same chassis) ...I know MAC addresses are used, of course, but arent the ethernet packets tagged internally? The switch does not only look at destination MACs to make switching decsions, it would also have to look at the internal (?) vlan tag because it will not L2 switch traffic between vlans, of course...

If someone has a nice little doc that explains it, let me know, please...

I have this problem too.
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Nagaraja Thanthry Wed, 07/07/2010 - 17:19

I think the switch does not tag the traffic within the switch. However, it does use the VLAN information along with the MAC address to determine the destination port.

http://www.cisco.com/networkers/nw03/presos/docs/RST-2011.pdf

Based on the above presentation from Cisco, the VLAN information and the MAC address is used to lookup the TCAM entry that decides the exit port.

Hope this helps.

Regards,

NT

Note: Please rate useful posts.

lamav Thu, 07/08/2010 - 08:02

NT: This is an excellent documet. I havent read it all yet, but its great so far.

Thank you very much for sharing.

And if you have any other good stuff like this, please share some more!

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