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Cisco AVVID Network Infrastructure IP Multicast Design - page 44 / 98





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Chapter 3

IP Multicast in a Wireless LAN

IP Multicast WLAN Configuration

If IP Multicast is to be deployed and streamed across the wireless network, then the following recommendations should be implemented:

Prevent unwanted multicast traffic from being sent out on the air interface.

  • Place the WLAN in its own subnet.

  • Control which multicast groups are allowed by implementing multicast boundaries on the egress

Layer 3 interface connecting to the VLAN or interface to the AP or bridge.

To gain the highest AP/bridge performance for multicast traffic and data traffic, configure the APs and bridges to run at the highest possible fixed data rate. This removes the requirement for multicast to clock out at a slower rate, which can impact the range of the AP/bridge and must be taken into account in the site survey.

If multicast reliability is a problem (seen as dropped packets), ignore the preceding recommendation and use a slower data rate (base rate) for multicast. This gives the multicast a better signal-to-noise ratio and can reduce the number of dropped packets.

Test the multicast application for suitability in the WLAN environment. Determine the application and user performance effects when packet loss is higher than that seen on wired networks.

IP Multicast WLAN Configuration

The ip multicast boundary command configures an administratively-scoped boundary on an interface for multicast group addresses found in the range defined by an access list. No multicast packets are allowed to flow across the boundary from either direction, except those packets explicitly allowed by the access list.

Controlling IP Multicast in a WLAN with Access Points


Figure 3-1 shows the topology for a WLAN using an AP. The IP multicast source is the IP/TV server

        • (

          . There are two multicast streams being sourced from the IP/TV server.


          is a high-rate (1.4 Mbps) video stream.


          is a low-rate (100 Kbps) video stream.

The low-rate stream is allowed and the high-rate stream is disallowed on the WLAN link. A multicast boundary is used to control multicast forwarding and IGMP packets.

IP multicast configuration for the campus is covered in Chapter 2, “IP Multicast in a Campus Network.”

Cisco AVVID Network Infrastructure IP Multicast Design



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