Cisco VTP (Virtual Truking Protocol) Tutorial With Examples
This is my first post about my CCNP journey. I have all ready pass Routing exam. Now I am working on Switching. So my post would be about Switching for a period of time. To day I will write about VTP protocol. There is a lot of articles about VTP but I want to describe it from my point of view to understand it better.
VTP (Virtual Trunking Protocol) is used to manage vlan info (addition,deletion, …) between switches that reside in an area. It workes on layer 2. If correctly configured managing vlans in the domain is very easy. Domain is a collecion of switches that is configured with the same domain name. Adding a vlan to a switch will result the creation of the same vlan in other switches which are in the same domain.But in order to get updates we should configure domain and password. Domain is not related any other system like Windows Domain. It is just used in VTP nothing another else. Vlan trunking Protocol have versions. These are 1,2,3 but 3 is compatible with 1,2 and 2 compatible with
Now the vlan info can be exchanged. Vtp info has a version number after a change the SW which make change increments current version number and then disseminate vlan info with new version number. If we add a SW into the domain which have previous vtp database (which holds vlan info and version) and if his version is bigger then the domain, the new sw vlan info override current domain vlan info. To avoid this you should double check the vtp database.The best way is to delete database file which resides on sw disk named vlan.dat.
Remove directory filename [vlan.dat-0000]? yes
Delete unix:yes? [confirm]
Switches which have VTP have 4 modes in the domain.
Server mode: Server mode is given to switches to manage vlans. Server mode add,delete and change vlan info. After the operation the info is disseminated into other switches in the same domain.
Client mode:This mode is like read only mode. This type of switches just get vlan info and then send it other switches. It updates its vlan database according to this info. In VTP version 1and 2 vlan info resides in ram but in version 3 it is saved in to nvram.
Transparent mode: In version 1 updates doesn’t disseminated, but in version 2&3 updates are disseminated. But updates doesn’t used to update vlan database. Transparent switch doesn’t use or modify domains vlan info. Transparent switches can use vlan database in its own and his vlan database doen’t used by other switches. There are extended and private vlan issues but I will not cover them here. In this mode created vlans are stored in running and startup configurations.
Off mode: This mode is like transparent mode, but in this mode vtp updates doesn’t disseminated.
Vtp pakets is advertised by sending packets to reserved multicast address in through trunk links. So there is no advertisement in nontrunk(tagged) links.
These are global info about update packet means all packets own this infos;
VTP domain name
VTP configuration revision number
Update identity and update timestamp
MD5 digest VLAN configuration, including maximum transmission unit (MTU) size for each VLAN.
And these area about vlans
VLAN IDs (ISL and IEEE 802.1Q)
Additional VLAN configuration information specific to the VLAN type
In Vtp version 3 also includes
Primary server ID
An instance number,
Vtp operates by default in version 1. You should decide which version to use.
Vtp pruning eliminates unused vlans to disseminate through domain. Vtp pruning is not enabled by default. Vlans between 2-1001 are pruned by default but you can change pruning-list.
Here is some default Vtp defaults.
VTP domain name
MSTP database mode
VTP version 3 server type
Vtp information is saved into vlan database but if the switch is in transparent mode it is saved into running confiuration. Switches in transparent mode do not exchange update information.
Password configuration is not neccary but if used in domain all exchaging switches should configuration with password.
[VTP VERSION TRANSITION RULES]
Vtp version 1-2 does not support extanded and privates vlans so to create the type of vlans the switch should be in transparent mode.
If in version 3 extended vlans are configured can not change to lower versions.
After setting domain name it can not be removed.
Setting domain name
SW1(config)#vtp domain ismailbaydan.com
Changing VTP domain name from a to ismailbaydan.com
We changed our domain name from a to ismailbaydan.com
SW1(config)#vtp password ismail ?
hidden Set the VTP password hidden option
secret Specify the vtp password in encrypted form
SW1(config)#vtp password ismail hidden
Here there is two type of password hidden and secret. Secret is hashed version of password so to make it easy we chose hidden.
Setting vtp mode
SW1(config)#vtp mode ?
client Set the device to client mode.
off Set the device to off mode.
server Set the device to server mode.
transparent Set the device to transparent mode.
SW1(config)#vtp mode server
Device mode already VTP Server for VLANS.
Switch says “Device mode is allready VTP Server for VLANS.” because previous mode was server too. We can shutdown VTP with off mode
Setting vtp version
SW1(config)#vtp version ?
<1-3> Set the administrative domain VTP version number
SW1(config)#vtp version 3
VTP version is already in V3.
It says there is 3 version and we chose version 3 which is allready set 🙂
SW1(config)#vtp pruning ?
Pruning switched on
Switch on it
Port based vtp configurations
On a trunk port vtp can be turned on or off but only in version 3
SW1#sh vtp counters
Summary advertisements received : 0
Subset advertisements received : 0
Request advertisements received : 0
Summary advertisements transmitted : 0
Subset advertisements transmitted : 0
Request advertisements transmitted : 21
Number of config revision errors : 0
Number of config digest errors : 0
Number of V1 summary errors : 0
VTP pruning statistics:
Trunk Join Transmitted Join Received Summary advts received from
—————- —————- —————- —————————
Et0/0 52 29 0
They are generally related to packet counts
Vtp on each interface
SW1#show vtp interface
Interface VTP Status
Show vtp status on each interface
SW1#show vtp password
VTP Password: 182A9AFD19560209C84AC9E570C9C61D
Because we set it hidden it looks like this
General information about vtp
SW1#show vtp status
VTP Version capable : 1 to 3
VTP version running : 3
VTP Domain Name : ismailbaydan.com
VTP Pruning Mode : Enabled
VTP Traps Generation : Disabled
Device ID : aabb.cc00.0100
VTP Operating Mode : Server
Number of existing VLANs : 6
Number of existing extended VLANs : 0
Maximum VLANs supported locally : 4096
Configuration Revision : 0
Primary ID : 0000.0000.0000
Primary Description :
MD5 digest : 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
VTP Operating Mode : Transparent
VTP Operating Mode : Transparent
All info about vtp