The Lazy Networker

When VLANs are not propagating correctly in a VTP environment, it’s important to check for misconfigurations. Below are common issues and troubleshooting steps.

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1. Check VTP Mode and Domain Name

Issue: VLANs are not syncing between switches.

Solution:

• Ensure all switches have the same VTP domain name and password:bashCopyEditshow vtp status
  • If the domain name is different, update it:bashCopyEditvtp domain MyNetwork
• Ensure the VTP mode is correct (at least one switch should be in server mode).bashCopyEditvtp mode server

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2. Verify Trunk Links

Issue: VTP advertisements are not passing between switches.

Solution:

• Check if the trunk is up and operational:bashCopyEditshow interfaces trunk
• If a port is not in trunk mode, enable it:bashCopyEditinterface GigabitEthernet0/1 switchport mode trunk switchport trunk allowed vlan all exit
• Ensure Native VLAN matches on both ends of the trunk:bashCopyEditshow interfaces trunk
  • If needed, change it:bashCopyEditswitchport trunk native vlan 99

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3. Check VTP Version

Issue: Switches running different VTP versions may not sync.

Solution:

• Check the VTP version:bashCopyEditshow vtp status
• If versions do not match, change them:bashCopyEditvtp version 2

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4. Check VTP Revision Number

Issue: A newly added switch with a higher revision number could erase VLANs.

Solution:

• Check the VTP Revision Number on all switches:bashCopyEditshow vtp status
• If a switch has a high revision number but incorrect VLANs, reset it:bashCopyEditvtp mode transparent vtp mode server # (or client if required)
  • This resets the revision number to 0.

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5. Verify VTP Pruning

Issue: VLANs are not being propagated to all switches.

Solution:

• Check if VTP pruning is enabled:bashCopyEditshow vtp status
• If necessary, disable VTP pruning:bashCopyEditno vtp pruning

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6. Check VTP Password

Issue: If a password is set on one switch but not on others, VLANs won’t sync.

Solution:

• Check if a VTP password is set:bashCopyEditshow vtp password
• If needed, set the same password on all switches:bashCopyEditvtp password Cisco123

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7. Test VLAN Synchronization

Issue: VLANs still not syncing after troubleshooting.

Solution:

• Try manually adding a VLAN on the VTP server and check if it propagates to the clients:bashCopyEditconfigure terminal vlan 50 name Test_VLAN exit
• Then verify on a client switch:bashCopyEditshow vlan brief
  • If the VLAN does not appear, go through the previous troubleshooting steps again.

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Summary of Key Troubleshooting Commands

Command	Description
show vtp status	Displays VTP domain, mode, revision number, and version.
show vtp password	Checks if a VTP password is set.
show interfaces trunk	Verifies if trunks are correctly configured.
show vlan brief	Checks if VLANs are propagating.
vtp mode transparent → vtp mode server	Resets the VTP revision number.

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Best Practices to Avoid VTP Issues

✅ Use VTP Transparent Mode unless central management of VLANs is necessary.
✅ Reset the revision number when adding new switches to the network.
✅ Secure VTP with passwords to prevent unauthorized VLAN changes.
✅ Monitor trunk links to ensure VTP messages are transmitted properly.