Interlogix GE-DSH-73 Series User Manual - Manual (Page 83)

Chapter 5: Web-Based Management
GE-DSH-73/DSH-82 and DSH-82-PoE User Manual 79
• Port VLAN ID
Packets that are tagged (are carrying the 802.1Q VID information) can be transmitted
from one 802.1Q compliant network device to another with the VLAN information
intact. This allows 802.1Q VLAN to span network devices (and indeed, the entire
network - if all network devices are 802.1Q compliant).
Every physical port on a switch has a PVID. 802.1Q ports are also assigned a PVID, for
use within the switch. If no VLAN are defined on the switch, all ports are then
assigned to a default VLAN with a PVID equal to 1. Untagged packets are assigned
the PVID of the port on which they were received. Forwarding decisions are based
upon this PVID, in so far as VLAN are concerned. Tagged packets are forwarded
according to the VID contained within the tag. Tagged packets are also assigned a
PVID, but the PVID is not used to make packet forwarding decisions, the VID is.
Tag-aware switches must keep a table to relate PVID within the switch to VID on the
network. The switch will compare the VID of a packet to be transmitted to the VID of
the port that is to transmit the packet. If the two VID are different the switch will drop
the packet. Because of the existence of the PVID for untagged packets and the VID
for tagged packets, tag-aware and tag-unaware network devices can coexist on the
same network.
A switch port can have only one PVID, but can have as many VID as the switch has
memory in its VLAN table to store them.
Because some devices on a network may be tag-unaware, a decision must be made
at each port on a tag-aware device before packets are transmitted - should the
packet to be transmitted have a tag or not? If the transmitting port is connected to a
tag-unaware device, the packet should be untagged. If the transmitting port is
connected to a tag-aware device, the packet should be tagged.
• Default VLANs
The Switch initially configures one VLAN, VID = 1, called "default." The factory default
setting assigns all ports on the Switch to the "default". As new VLAN are configured in
Port-based mode, their respective member ports are removed from the "default."
NOTE: No matter what basis is used to uniquely identify end nodes and assign these
nodes VLAN membership, packets cannot cross VLAN without a network device
performing a routing function between the VLAN.
The Switch supports Port-based VLAN and IEEE 802.1Q VLAN. The port untagging
function can be used to remove the 802.1 tag from packet headers to maintain
compatibility with devices that are tag-unaware.