Read a post about tagged, untagged VLAN and PVID.
There's two things you can set on the port for VLANs....tagged or untagged and PVID.
If
the port is set as untagged, then it tells the switch that the
device(s) connected to that port are VLAN unaware, so any packet to be
forwarded from that port out of the switch must be forwarded with the
VLAN tag removed. If the port is set as tagged, then the destination
device is VLAN aware, and packets will be forwarded with VLAN tags...so
tagged /untagged is for packets leaving the switch.
Now
for packets arriving at the switch port....if the packet arrives with a
VLAN tag , then - providing that port is in the VLAN matching the tag -
the packet will be forwarded; so if you have set a server NIC for
instance to apply a VLAN ID , then the packet arriving at the port will
be tagged...so in this case you have a VLAN aware device forwarding
packets already tagged , so you would configure the port into the
appropraite VLAN as a tagged port. Note that if the packet arrives at
the port tageed for a VLAN of which the port is not a member, the
switch will drop the packet.
If a packet arrives
at the port from an end device carrying no VLAN tag, then the switch
will add a VLAN tage which corresponds to the PVID, and then forward it
within that VLAN; so the PVID mechanisim allows you to have traffic
originating from a non-VLAN aware device to become an 802.1q packet, so
that it can traverse to other switches and still be contained within the
correct VLAN; so PVID is for non tagged packets arriving at a port on
the switch.
