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VLAN Trunking Protocol (VTP)


The basic goals ofVLAN Trunking Protocol (VTP)are to manageall configured VLANs across a switched internetwork and to maintain consistency throughoutthat network VTP allows you to add, delete, and rename VLANs—information that is thenpropagated to all other switches in the VTP domain.

VTP Modes of Operation


Server

This is the default mode for all Catalyst switches. We need at least one server in your VTP domain to propagate VLAN information throughout that domain. Also important: The switch must be in server mode to be able to create, add, and delete VLANs in a VTP domain.VTP information has to be changed in server mode, and any change made to a switch in server mode will be advertised to the entire VTP domain. In VTP server mode, VLAN configurations are saved in NVRAM.

Client

In client mode, switches receive information from VTP servers, but they also send and receive updates, so in this way, they behave like VTP servers. The difference is that they can’t create, change, or delete VLANs. Plus, none of the ports on a client switch can be added to anew VLAN before the VTP server notifies the client switch of the new VLAN. Also good to know is that VLAN information sent from a VTP server isn’t stored in NVRAM, which is important because it means that if the switch is reset or reloaded, the VLAN information will be deleted. Here’s a hint: If you want a switch to become a server, first make it a client so it receives all the correct VLAN information, then change it to a server—so much easier!

So basically, a switch in VTP client mode will forward VTP summary advertisements and process them. This switch will learn about but won’t save the VTP configuration in the runningconfiguration, and it won’t save it in NVRAM. Switches that are in VTP client mode will onlylearn about and pass along VTP information.

Transparent

Switches in transparent mode don’t participate in the VTP domain or share its VLAN database, but they’ll still forward VTP advertisements through any configured trunk links. They can create, modify, and delete VLANs because they keep their own database one they keep secret from the other switches. Despite being kept in NVRAM, the VLAN database in transparent mode is actually only locally significant. The whole purpose of transparent mode is to allow remote switches to receive the VLAN database from a VTP server-configured switch through a switch that is not participating in the same VLAN assignments.

VTP Pruning

VTP gives you a way to preserve bandwidth by configuring it to reduce the amount of broadcasts, multicasts, and unicast packets. This is called pruning. VTP pruning enabled switches send broadcasts only to trunk links that actually must have the information.



Switch 0 configuration

Switch # Config terminal
Switch (Config) # vlan 10
Switch (Config) # vlan 20
Switch (Config) # vlan 30
Switch (Config) # vlan 40
Switch (Config) #vtp mode server
Switch (Config) #vtp domain cisco.com
Switch (Config) #vtp password cisco
Switch (Config) # interface fastEthernet 0/1
Switch (Config-if) #switchport trunk encapsulation dot1q
Switch (Config-if) #switchport mode trunk
Switch (Config) # interface fastEthernet 0/2
Switch (Config-if) #switchport trunk encapsulation dot1q
Switch (Config-if) #switchport mode trunk


Switch 1 configuration

Switch # Config terminal
Switch (Config) #vtp mode client
Switch (Config) #vtp domain cisco.com
Switch (Config) #vtp password cisco
Switch (Config) # interface fastEthernet 0/1
Switch (Config-if) #switchport trunk encapsulation dot1q
Switch (Config-if) #switchport mode trunk
Switch (Config) # interface fastEthernet 0/2
Switch (Config-if) #switchport trunk encapsulation dot1q
Switch (Config-if) #switchport mode trunk


Switch 2 configuration

Switch # Config terminal
Switch (Config) #vtp mode client
Switch (Config) #vtp domain cisco.com
Switch (Config) #vtp password cisco
Switch (Config) # interface fastEthernet 0/1
Switch (Config-if) #switchport trunk encapsulation dot1q
Switch (Config-if) #switchport mode trunk
Switch (Config) # interface fastEthernet 0/2
Switch (Config-if) #switchport trunk encapsulation dot1q
Switch (Config-if) #switchport mode trunk






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