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In this post we will see how multicast can be configured on WGB (workgroup bridge) solution. Here is the topology for this post. WGB (3502I) is connected to Autonomous AP (AAP2- 1131), where a wireled client (multicast receiver) is connected behind WGB. A multicast source is connected to L3 switch where all the SVI & DHCP pool defined.(VLC player is used to simulate multicast streaming & receving it at the other end)


AAP2 is connected to C3750  Fa1/0/12 which is configured as trunk port with native vlan 999.

interface FastEthernet1/0/11
 switchport trunk encapsulation dot1q
 switchport trunk native vlan 999
 switchport trunk allowed vlan 1,6,999
 switchport mode trunk
 priority-queue out 
 mls qos trust cos

Here is the config of Root AP (AAP1)

hostname AAP2
dot11 ssid WGB
   vlan 999
   authentication open 
interface Dot11Radio1
 ssid WGB
 station-role root
interface Dot11Radio1.999
 encapsulation dot1Q 999 native
 bridge-group 1
interface FastEthernet0.999
 encapsulation dot1Q 999 native
 bridge-group 1
interface BVI1
 ip address
ip default-gateway

Here is the config of WGB.

hostname WGB
dot11 ssid WGB
   authentication open 
interface Dot11Radio1
 ssid WGB
 station-role workgroup-bridge
 bridge-group 1
interface GigabitEthernet0
 bridge-group 1
interface BVI1
 ip address

Once you configure this you should see the WGB & its client association on AAP1 like below.

AAP2#sh dot11 associations 
802.11 Client Stations on Dot11Radio1: 
MAC Address    IP address      Device        Name            Parent         State     
001f.1618.dfec  WGB-client    -               44d3.caaf.4343 Assoc    
44d3.caaf.4343  WGB           WGB             self           Assoc

Now it is ready to test your multicast, I am streaming a video from PC1 to multicast group address & then from PC2 behind the WGB, joining to this group. Now if you do a wireless packet capture you could see the traffic going to across this link. Here is a sample output of that capture.


If you look at one individual packet in detail it will looks like this


You can see in the wireless frame header there are 4 different address (Receiver, Destination, Transmitter – AAP1 & Source – PC1). But both Receiver address & Destination address is same as the multicast MAC address. In other words these multicast frames are not acknowledged by WGB, so reliability of packet delivery cannot be ensured.

You can improved the reliability of multicast packet delivery by configuring WGB as infrastructure-client instead of normal client. You have to configure “infrastructure-client” command on root AP (AAP2) radio interface.

interface Dot11Radio1

Let’s see the difference it makes this time.


This time you can see each multicast frame is acknowledge by WGB. Here is the inside of a multicast packet this time.


You can see this time Receiver address is WGB mac address, so it is a unicast frame where WGB will acknowledge every time. The advantage is that if you have several clients behind the WGB, you send one broadcast (or one multicast), then a second copy of that broadcast/multicast encapsulated into a unicast frame to the WGB and the ACK from the WGB confirms that the frame was received and is going to be relayed to the wired clients. This increases reliability (usually, broadcasts and multicasts are never acknowledged)..

The downside is that it also increases traffic on the radio, as packets that are usually not acknowledged are now acknowledged (and you send as many unicast copies as you have WGBs). So the limitation of this mode is that the AP will not allow more than 20 WGB clients.

Normally in this scenario WGB receive same multicast frame twice. You can configure the workgroup bridge multicast mode to either “client” or “infrastructure” mode. If you configure it as “infrastructure” it will only accept 4 different MAC address frames & drop 3 MAC address frames (where destination & receiver address identical).

WGB(config-if)#station-role workgroup-bridge ?         
  multicast  configure multicast
  universal  Universal Client

WGB(config-if)#station-role workgroup-bridge multicast ?
  mode  configure multicast mode

WGB(config-if)#station-role workgroup-bridge multicast mo
WGB(config-if)#station-role workgroup-bridge multicast mode ?
  client          Client-mode accepts only 3-MAC address header mulitcast
  infrastructure  Infrastructure-mode accepts only 4-MAC address header

WGB(config-if)#station-role workgroup-bridge multicast mode client 
*Jul  6 19:55:34.932: %DOT11-4-UPLINK_ESTABLISHED: Interface Dot11Radio1, Associated To AP AAP2 0019.a945.fb00       
*Jul  6 19:55:35.526: %DOT11-6-MCAST_DISCARD: infrastructure mode multicast packets are discarded  in client mode  multicast mode

WGB(config-if)#station-role workgroup-bridge multicast mode infrastructure

In a future post we will see how we can do this when WGB is connected to Light Weight Access point as root.

Related Posts

1. Test Yourself- Basic Multicast
2. Configuring Multicast on WLC
3. Wireless Multicast is not working – Why ?
4. Understanding “VideoStream” feature
5. IGMP Basics
6. Multicast Address Allocation
7. Multicast Deployment Types
8. PIM-SM Static RP Configurations
9. PIM-SM Auto-RP configurations
10. PIM-BSR Bootstrap Router Configurations
11. Anycast with MSDP
12. PIM-SSM Source Specific Multicast