notes: VTP Vlan Trunking Protocol

VTP- Vlan Trunking Protocol - is a Cisco proprietary Layer 2 multicast messaging protocol that synchronizes VLAN information across all media types and tagging methods on your switches.

You must configure the VTP domain name identically on each device; domain names are case-sensitive.
1. The switches must be adjacent.
2. The switches must be connected with trunk links.
3. The same VTP password must be configured if used in the domain

Versions

Version3 - enhanced, supports the use of extended VLAN range.

Version1,2 - supports md5 authentication and pruning.

VTP has four possible message types:
1. Summary advertisements
2. Subset advertisements
3. Advertisement requests
4. VTP Join messages (used for pruning)


VTP Modes:

1. Server: Enables you to create, modify, and delete VLANs; these changes are advertised to VTP Client mode systems; Catalyst switches default to this mode.
- VLAN configuration is stored in the VLAN database file called vlan.dat and is located on flash (const_nvram).
- VLANs 2-1000 are configurable.

2. Client: Does not enable the creation, modification, or deletion of VLANs on the local device; VLAN configurations are synchronized from Server mode systems.
- VLAN configuration is stored in the VLAN database file called vlan.dat and is located on flash (const_nvram).

3. Transparent: Permits the addition, deletion, and modification of VLAN information, but the information resides only locally on the Transparent device; these systems forward advertisements from servers but do not process them.
- Transparent mode is needed to configure extended VLAN range (1006-4096).
-If the domain name matches the locally configured domain name, a VTP version-2 transparent switch will transparently relay
transmitted TLV updates between switches, but a VTP version-1 transparent switch will drop those TLV updates.
- VLAN add/removes in the VTP domain does not affect transparent switches as the updates are not stored.
- A revision of 0 indicates a transparent mode switch is not participating in the update sequence of the VTP domain.
Note: pruning will be problem w transparent in the middle of client server.

VTP Revision number

The VTP configuration revision number is important. This value determines whether a switch has stale information about VLANs and ultimately controls whether the switch overwrites its VLAN database with new information.
The revision number increments each time a change is made to the VLAN database on a Server mode VTP system. The number is from 0 to 4,294,967,295.

WARNING: When introducing new Server mode switches, ensure that you do not inadvertently overwrite the VLAN database because of a higher configuration revision number on the new switch. Introducing new switches in Transparent mode helps ensure that this problem never results.

command to configure VTP:

vtp mode server
vtp mode domain-name

Authentication
-domain name is required
-ensure that md5 and passwords are the same

command:

vtp password pwd

VTP Pruning - enables you to limit the amount of traffic sent on trunk ports. It limits the distribution of flooded frames to only switches that have members of the particular VLAN.
- Eliminates the need to statically remove VLANs from trunk links where they not needed, this is done by having the switches automatically communicate with each other which VLANs they have locally assigned or are in the transit path for.
- this also reduces broadcast traffic.
- all vlan are pruned by default except the default vlan1


command:

vtp pruning

- vtp pruning can be configured only on vtp server and it will automatically propagate within the vtp domain.

VTP Pruning eligible list
- select VLANs you choose prune-ineligible
- Removing a VLAN from the "prune eligible list" forces the switch to receive traffic for that VLAN.
- ONLY VLANs 2-1000 are "prune eligible", the 5 default VLANs (1, 1002-1005) and extended VLANs cannot be pruned off an interface.

example command:

switchport trunk pruning vlan 2-11,13-1001

- Vlan 10 removed from the prune eligible list means. So traffic for VLAN 10 will be received.