Page 23-1

23 Multicast VLANs

Multicast VLANs enable you to control the flooding of multicast traffic in your network. For
example, you can define a multicast VLAN for all users that want to receive CNN Newscasts or
any other video feed or combination of feeds.
You define the multicast traffic to be transmitted by specifying a multicast address. You define
the recipients of the multicast traffic by specifying ports and/or specific MAC addresses. The
members of a multicast VLAN consist of the ports specified to receive the multicast traffic and
the ports to which MAC address recipients are connected. Instructions for creating multicast
VLANs begin on page 23-4.
Note the difference between multicast VLANs and AutoTracker VLANs. In AutoTracker VLANs,
devices are assigned to VLANs by examination of the frames that originate from those devices.
The members of an AutoTracker VLAN consist of source devices that fit the VLAN’s policies
and the ports to which those source devices are connected.
There are several differences between the configuration of multicast VLANs and the configura-
tion of AutoTracker VLANs. The following is a summary of points to note when configuring
multicast VLANs:
• You can not configure routing for multicast VLANs. Multicast VLANs are independent broad-
cast domains for multicast traffic originating from a multicast address and transmitted to
one or more recipients.
• Multicast VLANs allow three rules: Port, MAC Address, and multicast policy.
• There is not a default multicast VLAN. Therefore, you can define rules for all 32 available
multicast VLANs. All ports (even those that eventually become part of a multicast VLAN)
start off in the standard AutoTracker default VLAN #1, but they only get assigned to a multi-
cast VLAN if you explicitly assign them to one.
• All multicast VLANs include the multicast policy. This policy specifies the multicast address.
You use the other two rules—Port and MAC Address—to define the destination of the
multicast traffic.