The number of currently defined VLANs in
the device. Though VLANs should be created
using contiguous VLAN IDs, this is not
mandatory. Gaps in the VLAN ID sequence may
also result from the deletion of existing
VLANs. Therefore, this value represents the
total number of VLANs in the device and should
not be used to indicate the highest VLAN ID
value currently in use.