What is VTP - VLAN Trunking Protocol?
Before APIs were available on Cisco platforms, configuring a network switch was a manual process. So, the VTP – VLAN trunking protocol was a blessing to network engineers as it reduces the administration in a switched network.
Suppose you are working in a large enterprise switched network using hundreds of switches. For each type of traffic, you will need separate VLANs. Now, these VLANs need to be created on all switches, which is a time-consuming task for the network admins.
So, to reduce the burden of provisioning VLANs on switches, CISCO came up with this solution: VTP – VLAN Trunking Protocol.
What is VTP?
VTP stands for VLAN trunking protocol. It is a Layer 2 messaging protocol that maintains VLAN configuration consistency by managing the addition, deletion, and renaming of VLANs within a VTP domain.
It is used to store and exchange the VLAN information with multiple switches throughout the network. We can modify the whole network from a single switch (server mode rather than going on every switch to apply or execute the configurations.
There have been 3 VTP versions to date, and these are:
VTP Version 1
- It supports the standard 1-1005 VLAN range.
- VTP v1 is the default version on cisco switches.
VTP Version 2
- Version 2 provides additional features like token ring support and a VLAN consistency check.
- VTP version 1 and version 2 are not compatible with each other.
VTP Version 3
- It is the most flexible version of all.
- It was built to forward VLAN and other database information such as MSTP.
- It supports the extended VLAN range, which is 1006-4094.
- VTP Versions 1 and 2 are limited to VLANs from 1 to 1005.
- The version 3 of VTP allows the full range of VLANs 1 to 4094.
- Server Mode
- It is the default mode on all CISCO Switches
- Here we can create, modify or delete VLANs
- It Syncs the VLAN information with other client switches
- Sends and forwards the advertisements
- Client Mode
- Not allowed to create, delete or modify the VLANs
- These clients switch only receive the advertisements from server switches and sync the database with the server switch according to (Configuration Revision)
- Transparent Mode
- A switch with VTP transparent mode doesn't participate in the VTP domain.
- It doesn't send or receive the VLAN database from VTP server switches, but it can pass the VLAN traffic to other switches connected to it via trunk links.
- VLANs can be created, deleted, and modified in this mode, but the VLAN database of this switch is not shared with any other switch in the network.
VTP uses a multicast address for advertising its updates across the trunk links to all the switches in the VTP domain.
Multicast Address 01-00-0C-CC-CC-CC
Three types of VTP Advertisements are their –
- Summary advertisement
- Sent out every 300 seconds
- It also includes the VTP version of the domain, the revision number for the configuration and date stamp.
- Subset Advertisement
- Sent out when there is a change in the VLAN database
- Client request
- This happens when a switch with a low revision number joins the VTP domain and observes a summary advertisement with a higher revision than stored locally in the VTP domain.
VTP advertisements consist of,
- VLAN ID
- VTP Domain Name
- VTP Password
- VTP configuration revision number
- VLAN configuration
Conditions to configure VTP
- Trunking should be done; else, traffic will not be forwarded to client switches.
- The same VTP domain and password should be there on all switches which are part of VTP
- VTP Version must match on all the devices
- VTP pruning eliminates the unnecessary broadcast or multicast traffic throughout the network.
- VLAN 1 cannot be pruned because it's the default VLAN
- Pruning is by default disabled on switches
VTP Configuration Revision Number
- VTP switches use an INDEX number known as a configuration revision number to keep track of the most recent information in the VTP Domain.
- The advertisement always starts with the configuration revision number that is 0 (Zero)
- When subsequent changes are made on a VTP server, the revision number is incremented before the advertisement is forwarded to the next switch.
Note: - Before adding a switch to the existing VTP Domain, ensure the new switch has VTP revision (0) because as long as the revision number is higher, the switch will accept the update from that switch which is having higher revision number.
Join our CCNA training for complete notes of the VTP. For more information, go to the CCNA training page. We hope you liked this blog. Do share your comments and suggestions in the comment box below.
Explore deeper depth to VTP in this video with our trainer Mr Abhijit Bakale.
FAQs about VTP (VLAN trunking protocol)
Question – What is VTP used for?
Answer - VTP is a CISCO proprietary protocol that is used to ensure consistency across the network. It is also used to synchronize the VLAN information within the VTP domain. It lets network administrators modify, remove and add VLANs which are then transmitted to other switches within the VTP domain.
Question – What is VTP and STP?
Answer – VTP stands for VLAN trunking protocol, whereas STP stands for Spanning Tree Protocol. VTP is the Cisco intellectual protocol used to transmit VLAN on the whole local area network. STP is a layer-2 network protocol, and it is used to prevent looping in a network topology.
Question – What is VTP mode?
Answer – There are 3 VTP modes: Server, Client, and Transparent. Server mode is the default mode for Cisco switches allowing for creating, adding, and removing VLANs. In the client mode, the clients switch only receives the advertisements from server switches. In contrast, in the transparent mode, the switch doesn't send or receive the VLAN database from VTP server switches, but it can pass the VLAN traffic to other switches connected to it via trunk links.
Question – What are the three modes of VTP?
Answer – The three modes of VTP are:
- Server mode – Switch in this mode can delete or add VLANs on its own.
- Client mode – A switch in this mode is not able to change its VLAN configuration.
- Transparent mode – A switch in this mode can send VTP advertisements but can't share its VLAN database.