VLAN Trunking Protocol allows a Network manager to configure a Switch so that it propagates the VLAN configuration to other Switches in the network.
A Switch is configure as Server which is the one in charge of propagating those changes to the other Switches that are configure in Client mode, more on that later.
Benefits of VTP:
- VLAN is consistent across the network.
- Accurate VLAN information.
- Dynamic reporting of added VLANs across a network.
- Dynamic trunk configuration when VLANs are added to the network.
- Domain : Consist of one or more inter-connected Switches that share VLAN configuration information using advertisements, a Router or a layer 3 Switch defines the boundary of a domain. All Switches in a domain have the same domain name.
One of the Benefits of having multiple domains is that VTP Domains limit the extent to which a configuration change propagates in the network, if an error occur only a part of the network would be affected.
- Modes: A Switch can be configured in one of the modes: Server, Client, Transparent.
- Server: It is the designated Switch to advertise the VTP information to other Switches, it can create, delete and modify the VLANs in the domain. It stores the VLAN information in NVRAM. By default all Switches are set in Server mode.
- Client: Cannot create, change, or delete VLANs, it stores the VLAN information only while the Switch is on.
- Transparent: These Switches forward the advertisements sent by the Server Switch but do not include then, they do not participate in VTP. They can create, rename and delete VLANs but VLANs created in these Switches are local to that Switch only.
The information is saved in NVRAM, which means that when the Switch reboots it does not default back to server mode.
- Pruning: Increases available Bandwidth by restricting flooded traffic to those trunk links that the traffic must use to reach the destination devices.
Default VTP Configuration:
- VTP Version = 1
- VTP Domain Name = null
- VTP Mode = Server
- Configuration Revision = 0
- VLANs = 1
VTP Version: VTP has three versions, 1, 2, and 3. All Switches in a domain must have the same version.
VTP Configuration Revision Number: It is use so that a Switch knows if the new information that it is receiving in a VTP advertisement is newer than the one it currently has stored. Th e revision number plays an important role in enabling VTP to distribute and synchronize VTP domain and VLAN configuration information.
The summary advertisement contains the VTP domain name, the current revision number, and other VTP configuration details.
Summary advertisements are sent:
- Every 5 minutes by a VTP server or client to inform neighboring VTP-enabled switches of the current VTP configuration revision number for its VTP domain
- Immediately after a configuration has been made
A subset advertisement contains VLAN information. Changes that trigger the subset advertisement include:
- Creating or deleting a VLAN
- Suspending or activating a VLAN
- Changing the name of a VLAN
- Changing the MTU of a VLAN
It may take multiple subset advertisements to fully update the VLAN information.
When a request advertisement is sent to a VTP server in the same VTP domain, the VTP server responds by sending a summary advertisement and then a subset advertisement.
Request advertisements are sent if:
- The VTP domain name has been changed
- The switch receives a summary advertisement with a higher configuration revision number than its own
- A subset advertisement message is missed for some reason
- The switch has been reset
Here are the Packet Tracer files i work with in this chapter: