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

    VLAN 1


      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

        • 1. Re: VLAN 1
          Pablo Barriga


          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.


















          • 2. Re: VLAN 1


            Hi Pablo,



            thanks, this was exactly the info I was looking for.









            • 3. 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,



              • 4. Re: VLAN 1
                Pablo Barriga
                • 5. 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.






                  • 6. Re: VLAN 1
                    Mark Curtis

                    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