AutoTracker VLANs
Page 22-9
How Devices are Assigned to AutoTracker VLANs (continued)

Port Policy Functionality

In release 2.1 and later, AutoTracker’s VLAN port policy can be set to operate in either of two
distinct modes:
• In the original mode, wherein membership in all VLANs active on a port is inherited by all
devices connected to that port. Original port policy functionality is explained on page
22-10.
• In a new mode, wherein membership in all VLANs active on a port is not inherited by all
devices connected to that port. This is the current, default functionality with which the
switch ships. Current port policy functionality is explained on page 22-11.
Port policy functionality is set on a switch-wide basis, via a flag in the switch’s mpx.cmd file
called reg_port_rule. The switch ships with port policy functionality set to operate in the new
mode. You can revert the switch to original port policy functionality by editing the file and
setting the reg_port_rule flag to 1. You must then restart the switch. (The file is accessed, and
can be edited, via the switch User Interface. You can view the current setting of reg_port_rule
with the view mpx.cmd command. See Chapter 7, “Managing Files,” for information on editing
the mpx.cmd file.)
Why the New Functionality?
Port policies can cause problems in a multi-switch environment. AutoTracker assumes that
each switch in a multi-switch environment can independently arrive at identical VLAN assign-
ments for all devices in the network. This is not true when port policies are in effect because
of their very nature: port policies are switch-specific and not network wide. The figure on
page 22-10, which explains original port policy functionality, provides an example of how
port policies can result in inconsistent VLAN membership between two switches – notice the
inconsistent VLAN membership in Omni Switch/Router 1 and in Omni Switch/Router 2.
The use of port policies in a multi-switch environment can result in connectivity problems if
the source switch and the destination switch are separated by other switches. The switches
along the path of the frame will not have identical VLAN memberships. At any particular
switch along the path, frames could be lost because of inconsistencies in the VLAN member-
ship of the frames’ source and destination devices.
In addition, AutoTracker maintains devices in the same VLAN without regard to the devices’
location – provided the devices match the same AutoTracker policies throughout the network.
Multiple switches will assign a device to the same VLANs provided that device matches the
same policies on each switch. This is not possible when port policies are in effect because, as
stated, by their very nature port policies are switch-specific and not network-wide.
For these reasons, the Omni Switch/Router now ships with new port policy functionality
(although, as explained, you can revert the switch to original port policy functionality if you
wish). The new functionality still enables users to assign ports to VLANs and still enables those
ports to carry traffic for those VLANs. However, with the new functionality, port policies are
not used to learn VLAN assignments for traffic received on ports (as explained on page 22-11).
In order for a device to be assigned to a VLAN, it must match an existing logical policy of the
VLAN. This is explained on page 22-13.
The Following Examples
The following pages provide examples of original and current port policy functionality. The
limitations of port policies become apparent if one tries to use port policies to create two
VLANs in these sample networks, one for Devices A and B and one for Devices C and D.