Configuration Guide Configuring IGMP Snooping
10.3.4 Multicast-to-Unicast Conversion
The multicast-to-unicast conversion function is available only in wireless environment. After the function is configured on a
wireless device, multicast packets between an AP and STAs are transmitted in unicast mode. The multicast-to-unicast
conversion function runs on the AP.
Working Principle
The following describes the working principle of multicast-to-unicast conversion from several scenarios in wireless
environment.
In fat AP mode, IGMP Snooping needs to learn and track user information. After multicast-to-unicast conversion is configured,
the wireless multicast fast forwarding module queries the users who need multicast-to-unicast conversion through the
interface provided by the multicast-to-unicast conversion module, and replaces the destination MAC addresses in multicast
packets of the users with the MAC addresses of STAs, and destination IP addresses with IP addresses of the STAs, and
then forwards the multicast packets in unicast mode.
In fit AP centralized forwarding mode, an AC, according to recorded user information, queries the WLAN ID and RADIO ID of
an STA for packets, conducts CAPWAP encapsulation on the packets, and then sends the packets to an AP. If the
multicast-to-unicast conversion is enabled, packets sent to the AP are delivered to the wireless multicast fast forwarding
module, which queries the interface of the multicast-to-unicast conversion module to learn about the users who need
multicast-to-unicast conversion. Then, the AP transmits multicast packets in unicast mode.
In fit AP local forwarding mode, after packets are forwarded to an AP, if multicast-to-unicast conversion is enabled, the AP
delivers the packets to the wireless multicast fast forwarding module, which transmit multicasts the packets in unicast mode.
Related Configuration
 Enabling the Global Multicast Function
By default, the global multicast function is disabled. Run the ip multicast wlan command to enable the global multicast
function. After global multicast is enabled, when an AC receives multicast packets, it conducts CAPWAP encapsulation on
the multicast packets and sends the packets to the AP associated with the AC in CAPWAP unicast mode.
Run the no ip multicast wlan command to restore default configuration. After global multicast is disabled, an AC directly
discards the received multicast packets.
 Enabling Multicast-to-Unicast Conversion
By default, multicast-to-unicast conversion is disabled.
In ap-config mode on an AC, run the igmp snooping mcast-to-unicast enable command to enable multicast-to-unicast
conversion, or on a fat AP, run the ip igmp snooping mcast-to-unicast enable command to enable multicast-to-unicast
conversion.
In ap-config mode on an AC, run the no igmp snooping mcast-to-unicast enable command to disable multicast-to-unicast
conversion, or on a fat AP, run the no ip igmp snooping mcast-to-unicast enable command to disable multicast-to-unicast
conversion.
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