802.1Q Vlan Segmentation; Sharing Resources Across 802.1Q Vlans - D-Link DES-3624 Series User Manual

There are two key components to understanding 802.1Q VLANs: Port VLAN ID numbers (PVIDs) and VLAN
ID numbers (VIDs). Both variables are assigned to a switch port, but there are important differences between
them. A user can only assign one PVID to each switch port. The PVID defines which VLAN a packet belongs
to when packets need to be forwarded to another switch port or somewhere else on the network. On the other
hand, a user can define a port as a member of multiple VLANs (VIDs), allowing the segment connected to it to
receive packets from many VLANs on the network. These two variables control a port's ability to transmit
and receive VLAN traffic, and the difference between them provides network segmentation, while still
allowing resources to be shared across more than one VLAN.

802.1Q VLAN Segmentation

The following example is helpful in explaining how 802.1Q VLAN segmentation works. Take a packet that is
transmitted by a machine on Port 1 that is a member of VLAN 2 and has the Port VLAN ID number 2
(PVID=2). If the destination lies on another port (found through a normal forwarding table lookup), the
Switch then looks to see if the other port (Port 10) is a member of VLAN 2 (and can therefore receive VLAN 2
packets). If port 10 is not a member of VLAN 2, then the packet will be dropped by the Switch and will not
reach its destination. If Port 10 is a member of VLAN 2, the packet will go through. This selective forwarding
feature based on VLAN criteria is how VLANs segment networks. The key point being that Port 1 will only
transmit on VLAN 2, because it's Port VLAN ID number is 2 (PVID=2).

Sharing Resources Across 802.1Q VLANs

Network resources such as printers and servers however, can be shared across 802.1Q VLANs. This is
achieved by setting up overlapping VLANs as shown in the diagram below.
In the above example, there are three different 802.1Q VLANs and each port can transmit packets on one of
them according to their Port VLAN ID (PVID). However, a port can receive packets on all VLANs (VID) that
it belongs to. The assignments are as follows:
38
1 2 3 4
Port
VIDs = 1
Workstations
Figure 5-4. Example of typical VLAN configuration
PVID
(Port VLAN ID)
1
1
1
2
2
3
VID
(VLAN ID)
1
Stackable NWay Ethernet Switch User's Guide
VLAN 3
VLAN 2
VLAN 1
5 6 7 8 9 10 11 12
Port
VIDs = 2
Port
PVID = 3
Network
Server
Ports
Port 1
Port 2
Port 3
Port 11
Port 12
Port 7
Member Ports
1,2,3,7
Graphics
Workstations
Switch Management Concepts