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Cisco Wireless LAN controllers (WLC) perform multicast in two methods.

1. Unicast Mode (WLC unicast every multicast packet to every access point associated to the controller). This mode is inefficient, but if your network does not support multicast, this is the only mode you can use.

2. Multicast Mode (WLC send multicast packet to a CAPWAP multicast group). This is much more efficient & the preferred method of enabling multicast.

So how do you enable multicast on a WLC. It is simple three steps process.

Step 1: Enable multicast on the controller globally.
Step 2: Configure the controller for multicast mode. In multicast mode you
need to configure CAPWAP multicast group address.
Step 3: Configure IGMP snooping (optional)

By using the WLC GUI, Choose Controller > Multicast to open multicast page. Tick “Enalbe Global Multicast Mode” check box. If you want to enable the IGMP snooping tick the “Enable IGMP Snooping” check box.

Choose Controller > General to configure AP multicast mode (multicast or unicast) & CAPWAP multicast group address(only for multicast mode). Use private multicast IP (239.0.0.0/8) for the group address, but avoid 239.0.0.x or 239.128.0.x as these overlap with the link local MAC addresses & flood out all switch ports. This group address cannot be used for any application in your network. If you have multiple controllers, configure different group address for different controllers.

If you want to do this by using WLC CLI here are the 3 commands require.

config network multicast global enable
config network multicast mode multicast multicast_Group_Address (in my example 239.255.255.1
config network multicast igmp snooping enable

If you want to change the default IGMP time-out (60s) & Query Interval (20s) you can use the below CLI command to do that.

config network multicast igmp timeout time_out_vlaue {30 – 7200 in Seconds}
config network multicast igmp query interval Value {15-2400 in Seconds}

To view the multicast groups in use by using GUI, you can choose Monitor > Multicast. You will see something below. In my example I am streaming a video by using VLC (see here how you can do that) to a multicast addres 239.255.255.100

In CLI you can use following commands to verify

(WLC1) >show network summary
RF-Network Name……………………….. mrn-ccie
Web Mode……………………………… Disable
Secure Web Mode……………………….. Enable
Secure Web Mode Cipher-Option High………. Disable
Secure Web Mode Cipher-Option SSLv2……… Enable
Secure Shell (ssh)…………………….. Enable
Telnet……………………………….. Disable
Ethernet Multicast Forwarding…………… Enable
Ethernet Broadcast Forwarding…………… Disable
AP Multicast/Broadcast Mode…………….. Multicast   Address : 239.255.255.1
IGMP snooping…………………………. Enabled
IGMP timeout………………………….. 60 seconds
IGMP Query Interval……………………. 20 seconds

(WLC1) >show network multicast mgid summary
Layer2 MGID Mapping:
——————-
InterfaceName                    vlanId   MGID
——————————– ——   —-
hqguest1                         11       8
hqvoice1                         15       9
management                       111      0
Layer3 MGID Mapping:
——————-
Number of Layer3 MGIDs……………………… 6
Group address    Vlan  MGID
—————  —-  —-
224.0.0.255      11    559
224.2.127.254    11    561
239.195.255.255  11    560
 239.255.255.100  11    565
239.255.255.250  11    563
239.255.255.255  11    562

(WLC1) >show network multicast mgid detail 565
Mgid…………………………………. 565 (this is the MGID for my streaming multicast group)
Multicast Group Address………………… 239.255.255.100
Vlan…………………………………. 11
No of clients…………………………. 1
Client List……………………………
Client MAC         AP Name                            Expire Time (mm:ss)  Multicast-Status           Qos User Priority
—————–  ———————————  ——————-  ————————-
00:1c:bf:96:80:3e  HQ-AP01                            0:41                 Normal Multicast           0

*** Keep following points as side notes ***

1. Controller always use the management interface for sending multicast packets (so management vlan for WLC should be multicast enabled).
2. Multicast application should not use UDP 5246, 5247 as this used by CAPWAP.Controller drops multicast packet to these port numbers.
3. When you enable IGMP snooping,WLC gather IGMP reports & create layer 3 MGID table & then send IGMP reports to switch (on behalf of clients) with a source address as the interface address on which it received the reports from wireless client.
4. When WLC receive multicast traffic to particular group, it forwards it to all the APs, but only those AP that have active clients subscribed to that multicast group.
5. Without IGMP snooping enabled, WLC always use Layer 2 MGID table
6. MGID is locally significant to a controller.

Related Posts

1. Test Yourself- Basic Multicast
2. Wireless Multicast is not working – Why ?
3. Understanding “VideoStream” feature
4. IGMP Basics
5. Multicast Address Allocation