VTP Pruning
By default, switches flood broadcasts, multicasts, and unknown unicasts across
trunk links. Suppose a host in VLAN 10 on Switch B sends a broadcast.
Hosts in VLAN 10 on Switch C need to see that broadcast, but Switch A has
no ports in VLAN 10, so it doesn’t need to receive the broadcast traffic.
Enabling VTP pruning causes the switch to keep track of VLAN port
assignments in its downstream switches. The switch then sends flooded
traffic only on trunks toward switches that have ports assigned to the VLAN
originating the traffic. It prunes flooded traffic from all other trunks. VTP
pruning increases the available bandwidth by preventing unnecessary traffic
on trunk links.
There are two versions of VTP: Version 1 and Version 2. To use Version 2,
all switches in the domain must be capable of using it. Configure one server
for Version 2, and the information is propagated through VTP. Version 2 has
the following added features:
■ It supports Token Ring VLANs.
■ Transparent switches pass along messages from both versions of VTP.
■ Consistency checks are performed only when changes are configured
through the CLI or SNMP.