Very Basic VLAN Question

Answered Question
Mar 6th, 2010
User Badges:

Hi,


I have what seems to be a very basic question, but even after doing many searches, and reading CCNP books,

I am not able to get a clear answer.



My Question :-


I have 3 switches   A <--> B <---> C, with links between A&B and B&C set as


                          switchport mode trunk

                          switchport allowed vlan all


           Switch B is in TRANSPARENT mode, 

           Switch A  (Server) and C (client) use VTP.


Switch A and C have VLAN 5 configured




Now, If I want traffic over VLAN 5 to pass from a host on Switch A through to a host on Swiych C, do I need to :-


                      MANUALLY configure  VLAN 5 on switch B ??????


Or will trunk traffic pass right through Switch B ?


Also, if switch B is non-cisco &  NON-VLAN aware, but can accept jumbo frames, will vlan  5 make it across from A to C ?


Thanks

Correct Answer by Jon Marshall about 7 years 4 months ago

Your'e not missing anything basic and it's a very good question.


I think the key issue here is it doesn't really make a lot of sense to have VTP server/client switches and then stick a VTP transparent switch in the middle. Either make all switches VTP transparent or use VTP Server/client on all switches. Mixing the 2 is as you say just creating more administration issues.


Personally i am a big fan of VTP transparent as it is inherently more secure and less easy to make a mistake with eg. overwriting the vlan database but in very large and dynamic environments there is a case for a VTP Server/client setup.


Jon

Correct Answer by Jon Marshall about 7 years 4 months ago


You need to have vlan 5 on the intermediate switch or traffic will not flow.


If switch B was non-vlan aware then only the native vlan would be allowed to pass so vlan 5 would have to be the native vlan on the trunk links.


Jon

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (2 ratings)
Loading.
Correct Answer
Jon Marshall Sat, 03/06/2010 - 11:50
User Badges:
  • Super Blue, 32500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN



You need to have vlan 5 on the intermediate switch or traffic will not flow.


If switch B was non-vlan aware then only the native vlan would be allowed to pass so vlan 5 would have to be the native vlan on the trunk links.


Jon

shahedvoicerite Sat, 03/06/2010 - 11:57
User Badges:

Thanks !!


That was my initial guess, but after reading more on Transparent mode, and how it "passes vtp advertisments",

I begin to wonder, what is the purpose of Transparent mode ??


I understand what it does, but whats the use of passing VTP information across, when it will break communication,

if the VLAN is not locally configured ??


I mean if you create a VLAN on A (Server) , and client C can see it, thats good.


       But if Switch C in the middle does not have it, then the VLAN will not be end-to-end.


       This will be a troubleshooting nightmare !!


Or am I missing something basic ??


Thanks

Correct Answer
Jon Marshall Sat, 03/06/2010 - 12:02
User Badges:
  • Super Blue, 32500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN

Your'e not missing anything basic and it's a very good question.


I think the key issue here is it doesn't really make a lot of sense to have VTP server/client switches and then stick a VTP transparent switch in the middle. Either make all switches VTP transparent or use VTP Server/client on all switches. Mixing the 2 is as you say just creating more administration issues.


Personally i am a big fan of VTP transparent as it is inherently more secure and less easy to make a mistake with eg. overwriting the vlan database but in very large and dynamic environments there is a case for a VTP Server/client setup.


Jon

shahedvoicerite Sat, 03/06/2010 - 12:09
User Badges:

Thanks again Jon !!


I think one of the reason for Transparent mode is introducing a new switch into the network, and not messing up the

vlan database (??)            http://www.cisco.com/warp/public/473/vtp_flash/



As an aside, I did my CCVP a couple of years ago, and I am pretty sure that at that time, VTP and trunking was explained in

much more detail, then it is now in the new SWITCH course ware !!

Jon Marshall Sat, 03/06/2010 - 12:14
User Badges:
  • Super Blue, 32500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN

shahedvoicerite wrote:


Thanks again Jon !!


I think one of the reason for Transparent mode is introducing a new switch into the network, and not messing up the

vlan database (??)            http://www.cisco.com/warp/public/473/vtp_flash/



As an aside, I did my CCVP a couple of years ago, and I am pretty sure that at that time, VTP and trunking was explained in

much more detail, then it is now in the new SWITCH course ware !!


There are quite a few people on these forums who are not big fans of VTP


When you add a new switch it is actually worth changing the switch to transparent and then back to VTP client. This resets the revision number back to 0 but it doesn't mean you have to leave the switch as VTP transparent. The key point is that the revision number on the new switch must be lower than the current VTP server revision number or you can overwrite the VTP database.


Jon

Actions

This Discussion