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vlan ID ?

Answered Question
Nov 22nd, 2013
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Hello, I did a wireshark trace from the pc connected to my Cisco VOIP phone. See attached pic.

I am wondering why this trace of some phone traffic does not show the voice vlan that I have configured my phone to operate within ? It should reveal itself as part of the ethernet frame, right ?

I am sure there is an obvious reason.


Thanks kindly.

Attachment: 
Correct Answer by Joseph Martini about 3 years 8 months ago

Do you see the voice VLAN ID (802.1Q header) on any traffic in the capture?  Some NIC cards will not show VLAN tags, but if you can sometimes see dot1q headers in a packet capture from the same computer the computer NIC card should not be the issue.  The reason I ask if you see the VLAN ID in any traffic, is that I'm not sure if the phone passes on the VLAN tag when using "SPAN to PC Port" or not.  I'll check on this and get back to you.


Edit: After testing this out with a 7961, SPAN to PC port does forward the VLAN tag to my computer when doing a packet capture.

Correct Answer by lohit prasad about 3 years 8 months ago

as per my understanding access devices will not have trunk vlan info. This s correct only. EthII will nt have frame as pkt flow is between phone and pc. u shld c if pkt flow between switch and switch or switch & server.

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Correct Answer
Joseph Martini Sun, 11/24/2013 - 04:01
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  • Cisco Employee,

Do you see the voice VLAN ID (802.1Q header) on any traffic in the capture?  Some NIC cards will not show VLAN tags, but if you can sometimes see dot1q headers in a packet capture from the same computer the computer NIC card should not be the issue.  The reason I ask if you see the VLAN ID in any traffic, is that I'm not sure if the phone passes on the VLAN tag when using "SPAN to PC Port" or not.  I'll check on this and get back to you.


Edit: After testing this out with a 7961, SPAN to PC port does forward the VLAN tag to my computer when doing a packet capture.

Correct Answer
lohit prasad Sat, 11/23/2013 - 05:23
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as per my understanding access devices will not have trunk vlan info. This s correct only. EthII will nt have frame as pkt flow is between phone and pc. u shld c if pkt flow between switch and switch or switch & server.

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