6 Replies Latest reply: Oct 12, 2010 5:04 AM by Hardik RSS

    Extended-range Vlan!!!


      Hi All,


      I was refering CCNP_Switch book by CISCO, and i saw this statement there,










      Although the extended range of VLAN numbers enables you to support more

      VLANs in your network, some limitations exist. For example, a switch normally maintains

      VLAN definitions in a special database file, separate from the switch configuration.

      The VLAN Trunking Protocol (VTP) uses the VLAN database so that VLAN definitions

      can be advertised and shared between switches over trunk links. When extended-range

      VLANs are created, they are not stored in the VLAN database file.




      I was wondering about the statement marked in Red. It is saying that Extended-range VLANs are not stored in the VLAN database. Are there any specific reason for not having vlan info over Vlan.dat file? If not then where exactly it get stored for switch to refer?


      I also know that extended-range is only available in VTP Transparant mode, and as well in VTP version 3. So the second question aris is why it is not allowed in VTP client or Server Mode? 



      Thanking you in advance...





        • 1. Re: Extended-range Vlan!!!

          Any one??????????????????

          • 2. Re: Extended-range Vlan!!!



            as i know that when VTP transprent mode you can create extended vlan from 1006-4096, and will be saved on running-config and can be saved in startup-config, why its not saved in Vlan.dat becuase vlan Data Base not supported for extended Rang Vlan, ...


            i hope its helpful info.



            • 3. Re: Extended-range Vlan!!!

              Hi dude


              The only purpose I can think off is probably to stop the broadcast of these extended vlans within a VTP domain. and if its one of the reasons as I am sure the experts will correct it, then that is why you have to create it in the transparent mode and save it in the startup config, else the moment you reload the switch, the ext vlans will disappear.



              • 4. Re: Extended-range Vlan!!!




                Can any expert help me out with this confusion?







                • 5. Re: Extended-range Vlan!!!
                  Paul Stewart  -  CCIE Security

                  VTP is a Cisco thing.  Why they chose not to embrace the extended VLAN range with their VTP protocol is a question might have to be answered by someone in Cisco engineering or someone who has had a conversation with one of these people.  More specifically though this is not a question of why, but a question of why originally.  VTP versions 1 and 2 did not support the extended range, but VTP version 3 does support extended range vlans.  Who knows, maybe the original VTP versions only supported 10 bits in the VLAN field?

                  • 6. Re: Extended-range Vlan!!!

                    Hi Paul,


                    Gr8 to see your reply. But as fas as i know, VTP version 2 also support extended VLAN range, but only in VTP mode transperant. When you change the VTP mode from transoerant to Client or server mode, Extended VLAN data get deleted. So here comes the question of why. Why cisco has built such a scenario of ambiguity.


                    Also i guess VLAN bit was 12 bit only since then, as We see in VLAN trunking protocol 4 bit of priority and 12 bit of VLAN #, which evantually makes it of 16bit tag.


                    Some times i feel like, cisco has made many wonderful suspenses to create curiosity in us. Which makes us more hungry to know more and moe