VTP – VLAN Trunking Protocol (1.20)

VTP (the VLAN Trunking Protocol) cures the issues faced when configuring VLANs. Creating VLANs on one or two switches is easy enough, but as the scope of the VLANs increases managing each switch’s VLANs individually can become an administrative headache, and prone to mistakes and inconsistencies. Therefore a VLAN management protocol can make this much, much easier. 

VTP is one of a couple of VLAN management protocols, the others being GARP VLAN Registration Protocol (GVRP) these are defined in 802.1D (GARP) and 802.1Q (clause 11) for GVRP. These others are not currently supported by Cisco and are therefore not part of the Switch exam, or the CCIE exam.

VTP manages the addition, deletion, and renaming of VLANs across the network from a centralised point. It uses domains (areas with common VLAN requirements), and a switch can only belong to one domain. To participate in a VTP domain each switch must be in one of the following modes:
1. Server mode – this has full control over VLAN creation, deletion, and modification, this is the default mode for switches.
2. Client mode – cannot create, change or delete and VLANs. Clients listen to VTP advertisements from other switches and modify their own VLAN configuration. Also acts as a relay, forwarding VTP information to other switches.
3. Transparent mode – does not participate in VTP, and does not advertise its own VLAN configuration. With version 1 it does not relay VTP information from other switches unless the domain names and numbers match. In version 2 they can still act as relays regardless of the domain name.
VTP advertisements are sent using multicast and reference an index called the configuration revision number. The revision number starts at zero and increments by one with any change, at which point the update is sent to all VTP listening switches.
New switches should always be cleared of all VTP information before being introduced into the network.
Head back into the PacketTracer lab we created earlier and add the following:
Management domain:
switch0(config)# vtp domain test
switch1(config)# vtp domain test
switch0(config)# vtp mode server
switch0(config)# vtp version 2
switch0(config)# vtp password mypassword
switch1(config)# vtp mode client
switch1(config)# vtp version 2

switch1(config)# vtp password mypassword

Setting a VTP server
Setting a VTP client
Now we can add a couple of VLANs – so on Switch0 add VLANs 4 and 5, then do a “sh vlan” on Switch1
Create a VLAN
Without adding anything to Switch1 you should see 
show vlan
Running a “show vtp status” on switch0 you should see
show vtp status
VTP Pruning
Pruning makes more efficient use of trunk bandwidth by reducing unnecessary flooded traffic.
To implement this it is just a case of typing “vtp pruning” in config mode. But this is not supported in PacketTracer, at least not in the version I am running. It might be supported in future releases.
switch(config)# vtp pruning
Once this is added on the server, it is also enabled on the clients.
Troubleshooting VTP
Check the mode if updates are not being received – make sure not in transparent.
Makes sure at least one switch is set as the server.
Make sure trunks are used,  as advertisements are only sent over trunk links.
Make sure that the domain name is identical across all switches.
Versions should be compatible.
Passwords should match.