VTP Version 3

So with VTP v3 revision numbers no longer have any place which is great but am I correct in understanding that any switch in the VTP domain can become a primary server? What if i have 2 distro switches and X amount of access switches. Realistically I would want my vlan creations and my primary server on the DISTRO but what stops another administrator from promoting an access layer switch to primary?

Michael,
You can set a VTP v3 password that prevents a device from becoming primary without it. This is done via
(config)#vtp password <PASSWORD> hidden
Where the “hidden” keyword will obfuscate the password in the config.

Well that prevents any unauthorized switches from joining the VTP domain but once those switches agree on domain name and password what is to stop an administrator from choosing another switch other than the VTP primary and choosing that other switch as the VTP primary?

Actually,you helped me figure out thank you. You are correct in your reply I guess I just had a brain fart :slight_smile:

From the CISCO documentation - Thanks Andrew !!
http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3560/software/release/12-2_52_se/configuration/guide/3560scg/swvtp.html

Switch(config)# vtp password mypassword hidden
 Generating the secret associated to the password.
 Switch(config)# end
 Switch# show vtp password
 VTP password: 89914640C8D90868B6A0D8103847A733

Switch# vtp primary vlan
 Enter VTP password: mypassword
 This switch is becoming Primary server for vlan feature in the VTP  domain

 VTP Database Conf Switch ID      Primary Server Revision System Name           
 ------------ ---- -------------- -------------- -------- --------------------
 VLANDB       Yes  00d0.00b8.1400=00d0.00b8.1400 1        stp7                  

 Do you want to continue (y/n) [n]? y
Enabling the VTP Version

HI Rene,

There are an little error in this sentence:

Let’s see if we are able to synchronize some VLANs. We’ll start with something simple:

SW1(config)#vlan 100
SW2(config-vlan)#exit

I think its SW1 instead of SW2(config-vlan)#exit

Thanks for all! very easy to study with your explanations.

Thanks Luis, we will correct it.

Hi rene

What if we have VLAN MODE OFF - will ‘VTP mode off’ still support the extended VLANs / Private VLANs like transparent mode?

Any help is appreciated

Thanks

Hello Abhishek.

I’m not sure what you mean by VLAN MODE OFF. Do you mean VTP mode off? In any case, if I understand your question correctly, the VTP off mode allows you to turn off VTP either per port or globally. The difference between off and transparent modes is that transparent will forward VTP advertisements while off will not. Also, if it is turned off, normal-range, extended-range and private VLANS will not participate in VTP.

I hope this has been helpful!

Laz

19 posts were merged into an existing topic: VTP Version 3

Hi Laz,

I have topology S1–S2–S3 and I configured VTPv3 its working fine, but I tweaked and added VTP password for S1 and S3 but not S2 to find out if S2 will forward the VTP updates.

But I found that S2 its not forwarding the VTP updates to S3, is that normal or I’m missing something.

Regards
Jama

Hello Jama

Yes this is normal. If a switch is configured as a CLIENT with a specific VTP domain, then it will only forward VTP updates that are in its own domain. If you change the password, it cannot register to the VTP server and thus will not accept VTP updates from the specific domain (or from any domain), because it doesn’t properly belong to it. The only way to have a switch forward VTP updates is in transparent mode.

I hope this has been helpful!

Laz

1 Like

Dear Rene,

I am wondering what is the real difference between server (which is not a primary) and client modes in VTP v3? both cannot modify vlan information and both are propagating vtp updates ryt? what is the need of having those 2 modes??

Hello Roshan

The purpose of the two types of servers (secondary and primary) are to improve redundancy. Specifically, a secondary server stores the received configuration in a local permanent storage space (for example, NVRAM) and updates other devices in the same domain and for the same instance. In the event that the primary server fails, a secondary server can be promoted to be a primary server. More information about this procedure and its benefits over VTPv1 and v2 can be found in the following Cisco Documentation:

I hope this has been helpful!

Laz

1 Like

Hi Rene,

Can we enable VTP on a stack enabled switch or its only supported on Standalone switches.

Regards,
Selva.

Hello Selva

VTP functions on a switch stack just the same as it does on a standalone switch. When a siwtch joins the stack, it inherits the VTP and VLAN properties of the stack master, and all VTP updates are carried across the stack. You can find out more about how VTP functions on a stack by looking at this Cisco documentation.

I hope this has been helpful!

Laz

Hello Rene,
I was able to get my hands on a couple of old cisco switches. A 3750 and two 2960-s switches. While going throught the CCNP ENCOR 350-401 lab i was configuring the vtp version 3 across all 3 switches with the 3750 being the primary switch and the other two switches connected by trunk ports. I was able to create vlans and they populated fine to the other switches. When i created the private vlan on the 3750:

SW-A#sh vlan private-vlan
Primary Secondary Type              Ports
------- --------- ----------------- ------------------------------------------
500     501       community         Fa1/0/1
500     502       isolated

Everything looked fine, but on the 2960-s, even though vtp version 3 is supported the private vlan info is not. The vlans came across fine.

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
70   SERVERS                          active
500  VLAN0500                         active
501  VLAN0501                         active
502  VLAN0502                         active
-----------------------------------------------------------------------------
SW-B#sh vlan ?
  brief        VTP all VLAN status in brief
  group        VLAN group(s) information
  id           VTP VLAN status by VLAN id
  ifindex      SNMP ifIndex
  internal     VLAN internal usage
  mtu          VLAN MTU information
  name         VTP VLAN status by VLAN name
  remote-span  Remote SPAN VLANs
  summary      VLAN summary information
  |            Output modifiers

My question is, did i do something wrong? For private vlan configuration do all of the switches have to be the same model and running the same version of the ios? Does it have to be a layer 3 switch for private vlans to work? Or even though vtp version 3 is supported across all switches, just not all of the features.

C2960S Software (C2960S-UNIVERSALK9-M), Version 15.2(2a)E1, - client mode
C3750 Software (C3750-IPBASEK9-M), Version 12.2(55)SE10, - primary server

Rene’s comment:

Private VLANs: if you have VLANs that are configured as private VLANs then you can synchronize them with VTPv3.

Hello Cecil

It looks like you did everything correctly. After spending some time on VIRL and experimenting with various combinations, I was unable to replicate your results. I looked in the command reference for the specific IOS versions, and private VLANs as well as VTP3 are supported. However, I did go into checking for platform support for PVLANs and found that the 2960 does not support private VLANs. Take a look at this document:


The 2960 does not support PVLANs while the 3750 does, so this is the reason for this behaviour in your topology. :frowning:

I hope this has been helpful!

Laz

Hello Lagapides,
Thanks for the update to clear this up.

Cecil

1 Like

Just so you all know, in GNS3 using the IOU L2 switch once adding in VTP version 3 authentication, i had to re-enrol the primary server again and enter in the original password.

IOU1#vtp primary
This system is becoming primary server for feature vlan
Enter VTP Password:
No conflicting VTP3 devices found.
Do you want to continue? [confirm]
IOU1#
*Mar 10 23:30:56.455: %SW_VLAN-4-VTP_PRIMARY_SERVER_CHG: aabb.cc00.0100 has become the primary server for the VLAN VTP feature

Hi Matthew

This is great to know, thanks for sharing that!

Laz