Guidelines For Using Multicast Mode - Cisco 2100 Series Configuration Manual

Chapter 4 Configuring Controller SettingsWireless Device Access
When IGMP snooping is enabled, the following is true:
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The MGIDs are controller specific. The same multicast group packets coming from the same VLAN in
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two different controllers may be mapped to two different MGIDs.
If Layer 2 multicast is enabled, a single MGID is assigned to all the multicast addresses coming from an
Note
interface (see

Guidelines for Using Multicast Mode

Follow these guidelines when you enable multicast mode on your network:
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OL-17037-01
The controller always uses Layer 3 MGID for all Layer 3 multicast traffic sent to the access point.
For all Layer 2 multicast traffic, it continues to use Layer 2 MGID.
IGMP report packets from wireless clients are consumed or absorbed by the controller, which
generates a query for the clients. After the router sends the IGMP query, the controller sends the
IGMP reports with its interface IP address as the listener IP address for the multicast group. As a
result, the router IGMP table is updated with the controller IP address as the multicast listener.
When the client that is listening to the multicast groups roams from one controller to another, the
first controller transmits all the multicast group information for the listening client to the second
controller. As a result, the second controller can immediately create the multicast group information
for the client. The second controller sends the IGMP reports to the network for all multicast groups
to which the client was listening. This process aids in the seamless transfer of multicast data to the
client.
If the listening client roams to a controller in a different subnet, the multicast packets are tunneled
to the anchor controller of the client to avoid the reverse path filtering (RPF) check. The anchor then
forwards the multicast packets to the infrastructure switch.
Figure 4-12).
The Cisco Unified Wireless Network solution uses some IP address ranges for specific purposes,
and you should keep these ranges in mind when configuring a multicast group:
– 224.0.0.0 through 224.0.0.255—Reserved link local addresses
– 224.0.1.0 through 238.255.255.255—Globally scoped addresses
– 239.0.0.0 through 239.255.x.y /16—Limited scope addresses
When you enable multicast mode on the controller, you also must configure a CAPWAP multicast
group address. Access points subscribe to the CAPWAP multicast group using IGMP.
Cisco 1100, 1130, 1200, 1230, and 1240 access points use IGMP versions 1, 2, and 3.
Access points in monitor mode, sniffer mode, or rogue detector mode do not join the CAPWAP
multicast group address.
The CAPWAP multicast group configured on the controllers should be different for different
controllers.
Multicast mode does not operate across intersubnet mobility events such as guest tunneling. It does,
however, operate with interface overrides using RADIUS (but only when IGMP snooping is
enabled) and with site-specific VLANs (access point group VLANs).
Cisco Wireless LAN Controller Configuration Guide
Configuring Multicast Mode
4-35