VLAN Trunk Protocol – VTP Cisco – Explained
VTP or VLAN Trunking Protocol is a Cisco proprietary trunking protocol designed to reduce the burden of provisioning VLAN on the switch. For example, if you are working for an organization with Cisco switches deployed in its environment & you need to configure VLAN on all of them say 40 switches. What would you normally do is to login to each switch and create desired VLAN which is very time consuming and hectic task.
VTP has made this task very easy for network engineers / administrators as Cisco switches configured in VTP domain you just need to create VLAN on one switch ( with VTP server role ) & the switches which are configured in the same VTP domain can get their VLAN database updated from the server.
There are four VTP roles in this architechure. In order for VTP to work you need to setup VTP domain which must be same on all of your switches. Everytime you add, delete or modify any VLAN on VTP server, switches maintain configuration changes as revision numbers. Whenever a change is made revision number increases by 1.
Cisco switch configured as server is responsible for addition, deletion and / or modification of VLANs within VLAN domain. VTP supports multiple server in a VTP domain. These servers get synchronized from other servers like VTP clients.
switch1(config)#vtp version 3 switch1(config)#vtp domain CCNP switch1(config)#vtp mode server switch1(config)#vtp password CCNPENCOR
Cisco switch configured as VTP client receives VTP advertisements (sent every 300 sec ) from VTP server for addition, deletion and / or modification of VLANs. Please note that VLANs cannot be configured on VTP client locally all the necessary modification is done through VTP server.
switch3(config)#vtp version 3 switch3(config)#vtp domain CCNP switch3(config)#vtp mode client switch3(config)#vtp password CCNPENCOR
VTP Transparent Mode
Cisco Switches configured as transparent mode can not only receive but also forward VTP advertisements in the VTP domain. However you can configure VLAN locally.
switch2(config)#vtp version 3 switch2(config)#vtp domain CCNP switch2(config)#vtp mode transparent switch2(config)#vtp password CCNPENCOR
A switch does not participate in VTP advertisements and does not forward them to any ports. VLANs are provisioned locally.
We should be very careful while working with VTP as VTP server is also a VTP client!! As it can also get its VLAN database synchronized from other VTP client whose revision number is highest.
There are three versions of VTP. VTP version 1 is the default version & does not need to be configured. In VTP version 1 & 2, number of VLANs propagation is limited to 1005. However VTP version 3 allows full range (1-4096) of VLAN configuration. If a VTP domain is configured is version 3 and there are multiple VTP Servers, primary VTP server must be set.
Cisco VTP Advertisements
Cisco switches configured in a VTP domain advertises its updates across trunk links to all switches in VTP domain by using multicast address (01-00-0C-CC-CC-CC). VTP updates are sent out on trunk ports regardless of which VLANs are configured on the switches themselves. It doesn’t matter what VLANs are configured on them. So if you have two switches, one VTP server and one VTP client that are not directly connected that have the same VTP domain, version and password. In order for them to sync up their VLAN information, the intermediate switch(es) must either be transparent OR have the same VTP config. VTP is not affected by the initial VLAN configuration of the switches, either intermediate or not, either transparent or not.
There are three main types of VTP advertisements.
Summary advertisements occur every 300 or whenever a VLAN is added, removed or changed. These summary advertisements contain information regarding revision number, VTP domain, VTP version number & timestamp.
Subset advertisement occurs only when a VLAN configuration is changed. It contains information for switches to make changes to their VLAN database.
These advertisements orginate from VTP client to request more information on subset advertisement. This type of advertisement usually occurs when a new switch join the VTP domain (lower revision number) and it receives summary advertisement (having higher revision number), the client switch requests more details about the regarding specific VLAN.
That’s all for now, In this post we learnt about VTP (Cisco Proprietary Protocol) VTP. Hope this has been informative for you and you can learn about VLANs difference port type like Access Port & Trunk Ports here on our website.