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2239 Views 7 Replies Latest reply: Oct 12, 2012 6:07 AM by Angela RSS

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trunk port access mode

Oct 7, 2012 1:58 AM

jazz 22 posts since
Aug 23, 2010

Morning  people

 

Just wondering what is the purpose of trunk port access mode i just don;t get it. i get the part of normal switch

access port been assigned to certain vlan but for trunk port assigned to other vlans as well just not understanding it.

 

thanks

  • Najaf 111 posts since
    Sep 30, 2012
    Currently Being Moderated
    1. Oct 7, 2012 2:33 AM (in response to jazz)
    Re: trunk port access mode

    Hi Jazz,

     

    Are you sure that command is "trunk port access mode" ?? I have not seen any command like that before :-(

     

    Regards

     

    Najaf

  • ILKIN 13 posts since
    Mar 24, 2012
    Currently Being Moderated
    2. Oct 7, 2012 3:00 AM (in response to jazz)
    Re: trunk port access mode

    Hi Jazz!

    Do you mean somethink like the following config:

    interface FastEthernet0/1

    switchport access vlan 150

    switchport mode trunk

    switchport trunk native vlan 200

    If yes, then that config is needed when you connect your IP telephone directly to Fa0/1, and connect your pc to the phone. Assume that your voip vlan is 150 (ip telephones frames are tagged) and your regular vlan for pc is 200 (untagged). Thus we need a trunk port, passing all voip traffic with a tag 150, and regular traffic 200 untagged, i.e. native vlan. Obviously "switchport mode access" will not work, because only single vlan information will pass, but we need two.

  • Najaf 111 posts since
    Sep 30, 2012
    Currently Being Moderated
    3. Oct 7, 2012 3:34 AM (in response to ILKIN)
    Re: trunk port access mode

    Hi,

     

    I got consfused with your question :-)

     

    If your requirment is to connect IP phone to a switch port you dont necessarly need a trunk port. A typical configuration for ip phone would be as below.

     

    interface FastEthernet5/48

    switchport access vlan 120

    switchport voice vlan 111

    speed 100

    duplex full

    auto qos voip trust

    spanning-tree portfast

    spanning-tree bpduguard enable

     

    Here we use switchport voice vlan which will tag the voice traffic with VLAN  id of 111 and the data vlan is untagged.Cisco calls this a Multi-Vlan access port, and NOT a trunk port. if it were a trunk port, according to Cisco, it would flood all vlans configured on the switch out to the phone. A port configured for voice Vlan does not flood out all Vlans to the phone, just the voice vlan frames (tagged) and the data frames ( untagged )

     

    Below links give more details on the same.

     

    http://networkingnerd.net/2012/05/09/switchport-voice-vlan-post/

     

    Regards

     

    Najaf

     

    CCIE (R&S) 25070

  • Elvin Arias 1,855 posts since
    Mar 12, 2010
    Currently Being Moderated
    4. Oct 7, 2012 5:29 AM (in response to jazz)
    Re: trunk port access mode

    When you need to place an IP Phone on your network you normally separate the Voice VLAN from the Data VLAN in order to have more security, but with normal access mode on the switchport it's not recommended to do this. Because of that you can configure the switchport with the normal Data VLAN and at the same time associate the switchport to the Voice VLAN creating a special case trunk link. This allows the switchport to maintain both VLANs on the same switchport.

     

    Elvin

  • Currently Being Moderated
    5. Oct 7, 2012 8:36 AM (in response to ILKIN)
    Re: trunk port access mode

    I guess you are referring to the existence of the switchport access vlan statement if you have a trunk defined at the same time. In ILKIN's reply the "switchport access vlan 120" has no effect and is ignored because it is a simple trunk. If you change the trunk mode to  "switchport mode dot1q-tunnel" then this will be changed into a Q-in-Q trunk and the "switchport access vlan 150" will define the outer dot1q encapsulation. This is used in cases you want to tunnel multiple complete trunks separately through a single trunk and keep the trunks identified by the outer tag.

     

    HTH

  • Angela 746 posts since
    Jan 29, 2010
    Currently Being Moderated
    7. Oct 12, 2012 6:07 AM (in response to jazz)
    Re: trunk port access mode

    jazz, the trunk port is defined as a port that can and probably will handle traffic coming from multiple, different VLAN. So you can't really 'put a trunk port into a different vlan', you can only add traffic from a particular vlan to the overall traffic handled by the trunk port. And as others have pointed out already, the 'switchport access vlan x' command is ignored on the trunk port the port is doing QinQ tunnel, which is a whole different story.

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