Using HP-UX VLANs (September 2004)

Overview of Installation and Configuration
Special Case of VLAN ID 0--Priority Tagged Frames
Chapter 232
Special Case of VLAN ID 0--Priority Tagged
Frames
VLAN ID 0 means that the frame doesn’t belong to any VLAN but has
802.1p priority information. Ensure that any switches used with HP-UX
VLANs support VLAN ID 0.