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8076 Views 6 Replies Latest reply: Sep 7, 2008 1:14 AM by Mark Curtis RSS

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Aug 7, 2008 11:06 PM

0x2142 6 posts since
Jun 25, 2008

Hi all,






VLAN 1 is per default the native (=untagged) VLAN as well as the VLAN for CDP and other management protocols.



Since it´s possible to change the native VLAN, I wonder if the management VLAN changes as well or if the CDP information is still sent in VLAN 1 and if this can be changed.



In other words : Can I change the "management" VLAN from 1 to another as it is possible with the native VLAN ?












THX in advance

  • Pablo Barriga 84 posts since
    Jun 26, 2008
    Currently Being Moderated
    1. Aug 9, 2008 7:57 AM (in response to 0x2142)
    Re: VLAN 1


    Hello I ask the same to my trainer he told me that those protocols will still use vlan 1 to send their data.



    I found a deeper explanation on the book "Cisco LAN Switching Fundamentals: Configuring Switches"



    Here is an extract



    "It is important to remember that even when VLAN 1 is cleared from a trunk,

    the previously mentioned special traffic, such as CDP, PAgP, and VTP, is still

    forwarded across the trunk with a VLAN 1 tag, but no user data is sent using

    VLAN 1. All trunks default to a native VLAN of 1 unless changed. In the case of

    an 802.1q trunk, where the native VLAN is untagged, 802.1q IEEE Bridge Protocol

    Data Units (BPDUs) are forwarded untagged on the common spanning-tree VLAN 1 for

    interoperability with other vendors, unless VLAN 1 has been cleared from the

    trunk. Cisco Per-VLAN Spanning Tree (PVST+) BPDUs are sent and tagged for all

    other VLANs" By David Barnes, Basir Sakandar.

















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  • SpongeRob 81 posts since
    Jul 8, 2008
    Currently Being Moderated
    3. Sep 2, 2008 6:34 AM (in response to Pablo Barriga)
    Re: VLAN 1


    Hello Pablo,



    Then regarding CDP, pagp and other protocols that use vlan1 as a default - will they then use the newly defined native vlan ? and if Vlan1 is shut in favor of a new mangement vlan100 will those protocols then use the new management vlan?



    Trunking Regards,



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  • Pablo Barriga 84 posts since
    Jun 26, 2008
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    4. Sep 2, 2008 8:37 AM (in response to SpongeRob)
    Re: VLAN 1
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  • cnewby 75 posts since
    Apr 21, 2008
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    5. Sep 2, 2008 10:33 AM (in response to SpongeRob)
    Re: VLAN 1


    Hi Robb,



    Just want to clariry that special traffic (CDP, VTP, STP, PAgP etc) will always be sent across a trunk link either tagged as VLAN1 or untagged when VLAN is the native VLAN. So effectively (to my understanding) VLAN 1 is ALWAYS the management VLAN. This is because VLAN 1 can NEVER be removed/deleted etc.






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  • Mark Curtis 33 posts since
    Jul 10, 2008
    Currently Being Moderated
    6. Sep 7, 2008 1:14 AM (in response to cnewby)
    Re: VLAN 1

    This is a interesting discussion as I was actually asking myself the same question the other evening when reading up on this. So, if I setup ALL my switches and trunk ports on my switched network to use the default VLAN of 99, will i see my BPDUs and CDP all tagged with VLAN99 or untagged?



    There is also another interesting discussion on these forums here;





    Thanks folks

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