Cisco Cisco Access Registrar 4.2 Spécifications télécharger pdf (Page 129)

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Cisco Wireless LAN Controller Configuration Guide

OL-13826-01

Chapter 4 Configuring Controller SettingsWireless Device Access

Configuring Multicast Mode

If your network supports packet multicasting, you can configure the multicast method that the controller

uses. The controller performs multicasting in two modes:

• Unicast mode—In this mode, the controller unicasts every multicast packet to every access point

associated to the controller. This mode is inefficient but might be required on networks that do not

support multicasting.

• Multicast mode—In this mode, the controller sends multicast packets to an LWAPP multicast

group. This method reduces overhead on the controller processor and shifts the work of packet

replication to your network, which is much more efficient than the unicast method.

You can enable multicast mode using the controller GUI or CLI.

Understanding Multicast Mode

When you enable multicast mode and the controller receives a multicast packet from the wired LAN, the

controller encapsulates the packet using LWAPP and forwards the packet to the LWAPP multicast group

address. The controller always uses the management interface for sending multicast packets. Access

points in the multicast group receive the packet and forward it to all the BSSIDs mapped to the interface

on which clients receive multicast traffic. From the access point perspective, the multicast appears to be

a broadcast to all SSIDs.

In controller software release 4.2, Internet Group Management Protocol (IGMP) snooping is introduced

to better direct multicast packets. When this feature is enabled, the controller gathers IGMP reports from

the clients, processes them, creates unique multicast group IDs (MGIDs) from the IGMP reports after

checking the Layer 3 multicast address and the VLAN number, and sends the IGMP reports to the

infrastructure switch. The controller sends these reports with the source address as the interface address

on which it received the reports from the clients. The controller then updates the access point MGID

table on the access point with the client MAC address. When the controller receives multicast traffic for

a particular multicast group, it forwards it to all the access points, but only those access points that have

active clients listening or subscribed to that multicast group send multicast traffic on that particular

WLAN. IP packets are forwarded with an MGID that is unique for an ingress VLAN and the destination

multicast group. Layer 2 multicast packets are forwarded with an MGID that is unique for the ingress

interface.

Note IGMP snooping is not supported on the 2000 series controllers, the 2100 series controllers, and the Cisco

Wireless LAN Controller Network Module for Cisco Integrated Services Routers.

When IGMP snooping is disabled, the following is true:

• The controller always uses Layer 2 MGID when it sends multicast data to the access point. Every

interface created is assigned one Layer 2 MGID. For example, the management interface has an

MGID of 0, and the first dynamic interface created is assigned an MGID of 8, which increments as

each dynamic interface is created.

• The IGMP packets from clients are forwarded to the router. As a result, the router IGMP table is

updated with the IP address of the clients as the last reporter.

When IGMP snooping is enabled, the following is true:

• 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.

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