VALN locally assigned and VTP prunning and Domain

Question

I have got this scenario like this
Switch1:
vtp domain DOGCAT
vtp password CISCO
vtp pruning
vlan 3,5,6,8,10,26,33,52
Switch2:
vtp domain DOGCAT
vtp mode client
vtp password
Requirement:
VLANs not locally assigned should not be received over any trunk links throughout the VTP domain.
Explanation:
By default, all VLANs are allowed to be sent over any trunk link in the VTP domain. Therefore, broadcast frames and frames destined for unknown unicast addresses will be sent over all trunks throughout the domain. This behavior is undesirable when one or more switches throughout the VTP domain receive traffic for VLANs that they do not have locally assigned and are not in the transit path for.
In order reduce this unnecessary traffic VTP offers a feature known as pruning.
VTP pruning allows a switch to communicate with its directly connected
neighbors about what VLANs they have locally assigned and are in the transit path for.
Therefore VLANs that are unnecessary can be “pruned” off of the
interface. VTP pruning can be enabled by issuing the vlan database or global
configuration command vtp pruning.
I am looking to understand the concept of :
1- Can we consider vlan (3,5,6,8,10,26,33,52) locally ? If so why do we consider them localy,,,do we consider them locally because we define them under vlan command in global configuration ? or becaues they are in the same domain (DOGCAT) ?
2- ",,,, frames destined for unknown unicast addresses,,," ?!
3- " transit path for" ?

Answer 1

Hello,
I think your confusion might come from the term ´locally assigned´. To clarify this, conssider the following scenario:
You have 3 switches, Switch1, Switch2, and Switch3. All 3 switches are in the same VTP domain, so the configuration would look like this:
Switch1
vtp mode server
vtp domain CISCO
vtp password cisco
vlan 3,5,6,8,10,26,33,52
Switch2
vtp mode client
vtp domain CISCO
vtp password cisco
Switch3
vtp mode client
vtp domain CISCO
vtp password cisco
Now assume Switch2 and Switch3 are each connected to Switch1 by a trunk link.
VLANs can only be created on the VTP server, Switch1 in this case. The VLANs created on Switch1 are all propagated to Switch2 and Switch3, regardless of wether there is a port on those switches in up/up state assigned to one of those VLANs. Let´s say Switch2 has all ports assigned to VLAN 6 (that is, all ports are configured as following):
interface FastEthernet0/1
switchport access vlan 6
In this case, there would be no real need for all the other VLANs to be propagated to Switch2, because the only VLAN it needs is VLAN 6. This is where VTP Pruning becomes helpful. You enable it globally on the VTP server (Switch1 in this case), and all trunk links are checked for which VLANs are needed at the other end of the trunk connections, which are Switch2 and Switch3.
With regard to your specific question: VLANs 3,5,6,8,10,26,33,52 will be pruned if there are no ports assigned to those VLANs on the client switches (as stated in the example above). As a matter of fact, you cannot even create the VLANs on Swicth2 or Switch3, since they are in VTP client mode.
The only way Switch2 and Switch3 would be able to get the VLANS anyway is when they are configured as VTP servers as well. That might actually be your problem: the default VTP mode is server, that is why you can create VLANs and enable vtp pruning globally. Keep in mind that the VTP server always has the entire VLAN database, and that nothing is pruned off links between VTP servers...
Does that make sense ? Let me know if you still have doubts about the concept...
Regards,
GP