Alcatel Carrier Internetworking Solutions Omni Switch/Router - Manual (Page 675)

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
VLAN s as VLAN s 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 VLAN s as the source MAC
address. If the source MAC address is unknown, it is forwarded out all ports that have VLAN s
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 VLAN s unless an external router is between
those VLAN s. 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.