mac address table per vlan

[sarahr202]

hi every body!

Is there one mac address table for each vlan on a switch?

thanks a lot and have a nice day!

[John Blakley · Accepted solution]

You can do a show mac addre vlan and it will tell you what mac addresses are on that vlan.

--John

[nafdal123456]

jus sho mac addr is goog because i did sho mac addr vlan does not work 

thanks

[Jon Marshall · Accepted solution]

Sarah

Cisco switches support per-vlan mac-address tables. As posted by John you can show all the mac-addresses specific to a vlan and you can also clear all mac-addresses specific to a vlan.

Jon

[sarahr202]

thanks for your reply.

From my cisco press book, i get the impression there is one cam table which contains:

mac port vlan#

for example:

0000.1111.1111 port 11 vlan 1

0000.2222.2222 port 12 vlan 2

The point is all mac addresses are in one single cam table for every vlans.

when we use the command:

show mac address-table dynamic vlan 2

then the mac addresses belonging to vlan 2 in cam table will be shown.

Am i correct?

thanks a lot!

[Jon Marshall]

Sarah

I think it may well be the other way round on some switches (if not all). You actually have a per-vlan mac-address table but when you run "sh mac-address-table" the switch just combines them all into one output.

I don't know for sure if all switches support per-vlan mac-address tables.

Jon

[sarahr202]

thanks a lot for your reply Jon!

so when switch receives a frame, it first look at the vlan id to determine the corresponding mac address table to decide how to fooward the frame. Am i correct?

I was under the impression before i posted my question that switch use the mac address table which contains the mac addresss , vlans port to forward the frame.

Based on your response, it seems logical for a switch to first find the mac address table for particular vlan then forward the frame though my cisco book does not hint about it at all.

[John Blakley]

I misread the post. Jon's correct. It's:

vlan mac type port number

Sorry for my original response. :-)

--John

[Joseph W. Doherty]

Although a very old post, physically I strongly suspect there is but one MAC table that carries both the MAC and its corresponding VLAN.  Supporting this is datasheets will often list how many MACs might be stored on the switch without any mention of being tied to particular VLANs.  I.e. total MAC max regardless of number of VLANs, implying a shared resource.

Further, processing a single table where VLAN number is an attribute of a table tuple is considerably simpler then trying to tie together all the MACs within a specific VLAN, plus possibly using less resources to store the VLAN:MAC relationship.