User manual

AutoTracker VLANs
Page 22-12
The Usefulness of Port Policies
As has been explained – and as illustrated on page 22-10 – original port policy functionality is
not well-suited to the creation of consistent
VLAN membership in a multi-switch environment.
Current port policy functionality – as illustrated on page 22-11 – neither contributes to nor
participates in VLAN assignments. Port policies, either original or current, are in fact not useful
in the creation of consistent VLAN membership across multiple switches. Logical policies are
of far greater use, as illustrated on page 22-13. So, why use port policies at all?
Port Policies are Useful in these Situations:
•
Silent stations. If a device does not transmit traffic (such as a printer), the port to which the
device is connected never gets assigned to VLANs. It is then impossible for other stations to
communicate with that device. Creating a port policy that assigns the silent device’s port to
one or more VLANs will enable traffic to flow out that port to the silent device.
•
Inactive VLANs. AutoTracker does not activate a VLAN – or its internal router – until a port is
assigned to that VLAN. AutoTracker assigns ports to VLANs with port policies immediately.
However, AutoTracker only assigns ports to VLANs with logical policies when a frame is
received from a source device that matches the VLAN’s policies. This means that, in some
network situations, you may need to assign a port policy to a VLAN to force it active. Appli-
cation Example 5 in Chapter 24 provides an example of this.
•
Backbone connections. A port policy that assigns the backbone port to a VLAN will enable
traffic from that VLAN to flow out onto the backbone.
♦ Important Note ♦
If you are using port policies to extend VLANs across a backbone, you
are strongly advised to use current (default) port policy functionality. If
you use original port policy functionality, you are, in effect, placing all
devices learned from the backbone port into the same VLAN. If the port
policy is configured for all VLANs (so that all VLANs can communicate
over the backbone), all devices learned from the backbone port are
assigned to all
VLANs. This is not desirable – it would subject locally-
connected devices to all the backbone traffic.