Modular Ethernet Switch User’s Guide
28
Switch Management Concepts
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.
Figure 5-3. Example of typical VLAN configuration
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:
Port
PVID
Port 1
1
Port 4
1
Port 13
2
Port 16
2
Port 9
3
Ports
VID
1,4,9 1
9,13,16 2
1,4,9,13,16 3
Table 5-2. VLAN assignments for Figure 5-4
The server attached to Port 9 is shared by VLAN 1 and VLAN 2 because Port 9 is a member of both VLANs (it
is listed as a member of VID 1 and 2). Since it can receive packets from both VLANs, all ports can successfully
send packets to it. Ports 1 and 4 send these packets on VLAN 1 (their PVID=1), and Ports 13 and 16 send
these packets on VLAN 2 (PVID=2). The third VLAN (PVID=3) is used by the server to transmit files that
had been requested on VLAN 1 or 2 back to the computers. All computers that use the server will receive
transmissions from it since they are all located on ports which are members of VLAN 3 (VID=3).
802.1Q VLANs Spanning Multiple Switches
802.1Q VLANs can span multiple switches as well as your entire network. Two considerations to keep in
mind while building VLANs of this sort are whether the switches are IEEE 802.1Q-compliant and whether
VLAN packets should be tagged or untagged.
Definitions of relevant terms are as follows:
