Allowed, Active, and Pruned VLANs
Although a block can abutment VLANs 1–4094, several mechanisms abate the absolute cardinal of
VLANs whose cartage flows over the trunk. First, VLANs can be administratively banned from
existing over the block application the switchport block accustomed interface subcommand. Also, any
allowed VLANs charge be configured on the about-face afore they are advised alive on the trunk.
Finally, VTP can clip VLANs from the trunk, with the about-face artlessly abeyance to advanced frames
from that VLAN over the trunk.
The appearance interface block command lists the VLANs that abatement into anniversary category, as apparent in the
last command in Example 2-5. The categories are abbreviated as follows:
■ Accustomed VLANs—Each block allows all VLANs by default. However, VLANs can be
removed or added to the account of accustomed VLANs by application the switchport block allowed
command.
■ Accustomed and active—To be active, a VLAN charge be in the accustomed account for the block (based
on block configuration), and the VLAN charge abide in the VLAN agreement on the switch.
With PVST+, an STP instance is actively active on this block for the VLANs in this list.
■ Alive and not pruned—This account is a subset of the “allowed and active” list, with any
VTP-pruned VLANs removed.