[Day 9] 6. VTP (VLAN Trunking Protocol)

VLAN Trunking Protocol (VTP) is a Cisco proprietary protocol developed by Cisco Systems.

Definition & Purpose: VTP (VLAN Trunking Protocol) is used to manage VLAN configuration across switches in a network. It allows for the centralized administration of VLANs, ensuring consistency across multiple devices. VTP operates over trunk links, which carry traffic from multiple VLANs.

• Trunk Port: A port that carries traffic for multiple VLANs. It is used to connect switches or devices that need to communicate across multiple VLANs.

• Trunk Link: The physical link that connects trunk ports and is responsible for carrying VLAN-tagged traffic between switches.

• Access Port: A port that belongs to a single VLAN and is used to connect end devices like computers and printers.

• Trunks: Trunks are essential for allowing communication between devices in different VLANs over a single link. They are commonly used to connect switches and allow traffic from multiple VLANs to flow between them.

• VLAN ID Header: When packets travel over a trunk, a VLAN ID header is added to the packet to indicate which VLAN the packet belongs to. This header helps devices on the receiving end to correctly process the traffic.

• Tagging Methods: There are two common methods for tagging VLAN IDs on trunk links:

  • ISL (Inter-Switch Link): A Cisco proprietary protocol for tagging VLAN information.
  • 802.1Q: The industry-standard method for VLAN tagging.

Configuring a Trunk Link

The following steps configure a trunk link. Note that the 2900 series switches only support 802.1Q and do not support ISL.

1. Enter interface configuration mode for the desired port:
   

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   switch(config)# int g0/0

2. Set the port mode to trunk:
   

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   switch(config)# switchport mode trunk

3. Choose the encapsulation method (either ISL or 802.1Q):

   • For ISL:
     
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     switch(config)# switchport trunk encapsulation isl

   • For 802.1Q:
     
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     switch(config)# switchport trunk encapsulation dot1q

VTP (VLAN Trunking Protocol) Configuration**

VTP operates over trunk links and allows for the distribution of VLAN information between switches.

1. Set the VTP domain name:
   

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   switch(config)# vtp domain <Name>

2. Configure the VTP mode:

   • To allow the switch to create and modify VLANs:
     
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     switch(config)# vtp mode server

   • To allow the switch to only read VLAN information:
     
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     switch(config)# vtp mode client

   • To disable VTP and configure VLANs manually:
     
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     switch(config)# vtp mode transparent

3. (Optional) Set a VTP password for security:
   

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   switch(config)# password <password>