using voip and pc in same port

Unanswered Question
Sep 10th, 2007

Hi all, when we use voice phone and pc in the same port, I believe the pc traffic is normally untagged, but if I say use vlan 10 for the pc, if this is untagged along my trunk ports as its the native vlan, how does the next switch know the pc traffic is on vlan 10 ?

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 3 (1 ratings)
Loading.
carl_townshend Mon, 09/10/2007 - 08:16

but if the vlan is untagged on the access port by making it native, how is this tagged on the trunk port? as what would happen if I have say 3 different vlans for my clients, this would mean 3 different native vlans ?

Joseph W. Doherty Mon, 09/10/2007 - 09:26

"but if the vlan is untagged on the access port by making it native, how is this tagged on the trunk port?"

Normally it would remain untagged unless the switch supports some type of native to/from specified VLAN tagging feature.

"as what would happen if I have say 3 different vlans for my clients, this would mean 3 different native vlans ?"

If the frames remain untagged as it crosses between your switches, it would effectively become one VLAN. E.g. without tags, native VLAN10 on switch 1 would intermix with native VLAN20 on switch 2.

If you don't expect access devices to generate VLAN tags, then assign the port to a VLAN. The frames will have tags added/removed as they cross the switch's port.

szahid Mon, 09/10/2007 - 09:33

well , you will configure the native vlan of the trunk to be vlan 10 , and frame that does not have a tag is considered to be in native vlan ( in your case vlan 10 ) . So , a apcket coming from pc untagged ( in vlan 10 ) goes to the next switch , next switch sees the frame w/o a tag , it checks to see what is the native vlan of the port where the frame came in and it finds out that the native vlan is configured to be vlan 10 and the switch processes the frame in that vlan.

thanks

Salman.

Are you using Cisco Voice? If this is the case, you can copnfigure the ports differently, and the switch will use cdp to identify the phone and place traffic from the phone in the voice vlan.

int f1/0/1

switchport mode access

switchport access vlan 10

switchport voice vlan 20

spanning-tree portfast

mls qos trust cos

auto qos voip cisco-phone

no shut

Martin

Actions

This Discussion