VTP pruning is a function available in VLAN Trunking Protocol for Cisco products. It optimizes flooded traffic by saving and increasing available bandwidth. In the case of VTP pruning, this can be achieved by reducing the unwanted flooded traffic in form of broadcast, multicast and flooded unicast packets. The traffic is restricted by VTP pruning function to those trunk links which are needed by it in order to access the network devices. In that way, broadcast is not passed through trunk links which are not necessary for the correct operation and goes directly where it was destined to go. VLANs in Cisco switches are pruned from going to switches which do not have hosts for those VLANs. For example, if a switch does not have any ports in a particular VLAN, it does not receive the broadcast traffic thanks to described here feature.
VTP pruning function is disabled by default in Cisco switches, so you have to enable it in the configuration when you want it to be used on your device.
VTP pruning features:
1. VTP pruning reduces undesired broadcast and multicast flooded traffic
2. VTP pruning makes no changes to VLANs in a VTP domain (no modifications, no adding or deleting VLANs)
3. Default administrative VLAN 1 is pruning-ineligible (you cannot apply VTP pruning to VLAN 1)
Remember that one domain works with only one version of VTP (version 1, 2 or 3).
VTP pruning can be enabled globally on the Catalyst series switch, which makes it enabled for entire management domain. When you want to enable the VTP pruning on your Cisco switch, you have to use the VLAN configuration command. Once it is activated, there is a possibility to create your own list of pruning-ineligible VLANs, if you want to disable pruning for more than VLAN 1.
Useful commands:
1. vtp mode transparent – set the Cisco switch to transparent mode
2. vtp pruning – configure the VTP server in order to enable the VTP pruning
3. show interface – view the list of pruned VLANs
4. show vtp status – view the settings of VTP configuration
5. show interface trunk – view which VLANs are currently being forwarded down the trunk links while not pruned
VTP pruning function is disabled by default in Cisco switches, so you have to enable it in the configuration when you want it to be used on your device.
VTP pruning features:
1. VTP pruning reduces undesired broadcast and multicast flooded traffic
2. VTP pruning makes no changes to VLANs in a VTP domain (no modifications, no adding or deleting VLANs)
3. Default administrative VLAN 1 is pruning-ineligible (you cannot apply VTP pruning to VLAN 1)
Remember that one domain works with only one version of VTP (version 1, 2 or 3).
VTP pruning can be enabled globally on the Catalyst series switch, which makes it enabled for entire management domain. When you want to enable the VTP pruning on your Cisco switch, you have to use the VLAN configuration command. Once it is activated, there is a possibility to create your own list of pruning-ineligible VLANs, if you want to disable pruning for more than VLAN 1.
Useful commands:
1. vtp mode transparent – set the Cisco switch to transparent mode
2. vtp pruning – configure the VTP server in order to enable the VTP pruning
3. show interface – view the list of pruned VLANs
4. show vtp status – view the settings of VTP configuration
5. show interface trunk – view which VLANs are currently being forwarded down the trunk links while not pruned
