Troubleshooting Border Gateway Protocol (BGP)
Common Network Attack Strategies: Man in the Middle
Network Basics: Variable Length Subnet Masks (VLSM)

VLAN Trunking Protocol (VTP) Configuration Revision Number Management

The VLAN Trunking Protocol (VTP) revision number is important because it determines which updates are to be used when not managed properly this number can cause the deletion of all your networks VLAN information.

When you set a VTP Domain Name, the revision number is set to zero, after which each change to the VLAN database increases the revision number by one. When a switch receives VTP information from a neighboring switch, the first switch processes data only for the same domain when the revision number is higher than its own.

Always check your VTP revision numbers before adding a switch to your network or when adding a switch back to your network. If you remove a switch and place it in your lab, you may create additional VLANs or delete all configured VLANs — either of which will increase the revision number.

When you add that switch back into your production network, the switch will have the highest revision number of any device on the network. This forces the deletion of all existing VLANs to all other switches because they will have a lower revision number. Having all of your VLAN information deleted could be ruinous for your data network.

Always use show vtp status to check revision numbers. You can reset your revision number on the switch you are adding to the network by changing the VTP domain to something else and then changing it back.

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