trunk port identification from sh vlan command and unknown unicast frame

Unanswered Question
Jun 22nd, 2007


i have a question about trunk port used in vlans , the command sh vlan brief used on switches does not display trunk ports is is true kindly help ?

secondly when a switch receives a frame with destination mac address not in its mac-address table will this frame be forwaded to all its ports except the incoming port keeping in mind that ports of this switch are in different vlans .

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CSCO10892433 Sat, 06/23/2007 - 02:14

Hi, syed

The command "show vlan brief" will show you, for each vlan, the vlan name, vlan status and which ports are in this vlan. If you want to know which ports are the trunk ports, use "show interface trunk" command instead.

Unknown unicast frame in a specific vlan will be switched to:

1) all other access ports in the same vlan

2) all trunk ports in which this vlan is allowed and not pruned.

Please refer the following links:

sh vlan brief

sh interface trunk



syedsohailsarwar Sat, 06/23/2007 - 09:23


thanks alot

actually i was going through the dumps of CCNA from testking site and there was a question petaining to sh vlan command ans in its explanation it is saying the ports u dont see in sh vlan are trunk ports , thanks for updating me on using sh interface trunk command but was the first method right or wrong

actually there is one question asked in CCNA simulation where in u have to log into a switch and tell which ports are trunk ports

and secondly on which ports of that switch will unknown unicast will be broadcasted

hope u ll clear my doubt

syedsohailsarwar Sat, 06/23/2007 - 09:37

also i have one more question

CSU/DSU are used for digital or analog

termination i guess it might be digital termination

and what about modems are they used for digital or analog termnination


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