Allied Telesis AT-S24 - Manual (Page 104)

Configuring Virtual LANs and Quality of Service
104
The table below lists the ports assignments for the Sales and Production
VLANs:
The movement of traffic between the two VLANs is accomplished with a
router. The router has one connection to each VLAN. One router
interface is connected to port 6 on the switch, which is a member of the
Sales VLAN. Another router interface is connected to port 24, which is a
member of the Production VLAN.
There are, however, several drawbacks to port-based VLANs:
" It is not easy to share network resources, such as servers and
printers, across multiple VLANs. A router must be added to the
network to provide a means for interconnecting the port-based
VLANs.
" The introduction of a router into your network could create
security issues from unauthorized access to your network.
" A VLAN that spans several switches will require a port on each
switch for the interconnection of the various parts of the VLAN.
For example, a VLAN that spans three switches would require one
port on each switch just to interconnect the various sections of
the VLAN. In network configurations where there are many
individual VLANs that span switches, many ports can end up
being used ineffectively just to interconnect the various VLANs.
VLAN Tagging
The second type of VLAN supported by the switch is referred to as VLAN
tagging. The advantage of VLAN tagging is that you can easily share
network resources and at the same time retain the security found in
port-based VLANs. And when propagating the different VLANs
throughout the network, you only need one port-per-switch to trunk all
VLANs from one switch to another switch.
For these and other reasons, the IEEE developed additions to the 802
standards to accommodate VLAN tagging, the 802.1Q and 802.3ac
standards. VLAN tagging allows the user to define a VID for a given VLAN
traffic flow, and then use this VID to switch the traffic throughout the
network. This means that the user can have a device connected to a
switch port that can accept traffic from one or more VLANs.
The ability to allow a port to forward traffic from many VLANs instead of
only one (as in port-based VLANs) allows the user to overcome the port-
based limitations mentioned above. A server can now be configured to
accept the traffic from many different VLANs, and then return data to the
Sales VLAN (PVID 2) Production VLAN (PVID 3)
AT-8224XL Switch 1-6 19-24