This is probably a stupid question, but I am going to ask anyway.
If I enable pruning on a switch, compared to just adding the allowed VLANS on the trunk, is there a difference?
What would be the best way for the traffic to get to only the switch desired? Allowed vlans or enable pruning?
there is difference and it is the following:
be aware that VTP pruning can manage unnecessary flooding of multicast, broadcast, unknown unicast traffic but it does not limit the number of STP instances running on your switches.
switchport trunk allowed vlan list
has the added benefit to provide STP scalability by removing unneeded STP instances.
This has to be take in account if you use PVST+ or Rapid PVST.
20 vlans are not a problem but 130 vlans can be a problem for some low end switches.
also the limits on number of vlans can be different for VTP and for STP:
there are devices accepting up to 128 vlans in their VTP DB but only 64 STP instances.
The result that has been seen also in the forums are vlans with STP disabled without any human intervention!
(taken from my own post in a recent thread of today)
>> What would be the best way for the traffic to get to only the switch desired? Allowed vlans or enable pruning?
on the long term I prefer allowed vlans for the reasons explained above.
Hope to help
There is a difference.
With VTP pruning the vlan traffic is not sent across the trunk link if it is not needed but STP for that vlan still extends across the trunk link.
If you use the vlan allowed list if the vlan is not allowed on the trunk then STP does not extend across the trunk for that vlan.
Personally i prefer the allowed command but it does depend on how large your infrastructure is and how dynamic ie. how often are vlans needed and then not needed on switches.