AutoTracker VLANs
Page 22-15

Frame Flooding in AutoTracker VLANs

Flooding occurs when a frame is received addressed to a device that is unknown to the
switch or broadcast or multicast frames are received addressed to multiple users. In a typical
bridged environment, the frame would be forwarded out all ports. However, this is not true
with VLANs as VLANs segment the network into smaller broadcast domains. In this environ-
ment, flooding occurs as follows:
Unicast Traffic
• If the destination address of the frame is unknown buts its source address is known and
the source device is a member of one or more VLANs, the frame is flooded out all ports of
all VLANs in which the source device is a member. Please note the following:
– If the source device is a member of multiple VLANs, some leakage may occur during
the flooding process. Leakage may occur only among VLANs in the same Group—
frames do not leak between Groups.
– If the source device is a member of multiple VLANs and some or all of those VLANs
share the same physical port, only one copy of the frame is forwarded out that port.
– If the source device is a member of multiple VLANs that use trunking, only one copy
of the frame is sent to each trunk port.
• If both the source and destination addresses of the frame are unknown, the frame is
forwarded to the MPX for processing (to determine the VLAN or VLANs in which the origi-
nating device should be a member) and the frame is flooded out all ports of all VLANs in
which the source port is a member.
Broadcast and Multicast Traffic
Frames are forwarded out all ports that are members of the same VLANs as the source MAC
address. If the source MAC address is unknown, it is forwarded out all ports that have VLANs
active on the source ports.

Routing Between AutoTracker VLANs

Devices that do not share membership in a common VLAN must use routers to communicate
with one another. You can configure a virtual router port that is capable of IP and/or IPX
routing for each VLAN. By enabling a router port on a VLAN, you are creating a static route
entry within the switch to that VLAN. If this router port is not configured for a VLAN, then that
VLAN will not be able to communicate with other VLANs unless an external router is between
those VLANs. You may configure up to 16 virtual router ports within a single Omni Switch/
Router. Each VLAN may contain only one router port.
Routing and the Default VLAN. You can enable routing for the default VLAN when you initially
create a Group, or when you modify the Group. There are several issues about which you
should be aware when enabling routing on the Default VLAN. See Application Example 4 in
Chapter 24, “AutoTracker VLAN Application Examples,” for more information.