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15-11
Cisco IOS Software Configuration Guide for Cisco Aironet Access Points
OL-30644-01
Chapter 15 Configuring QoS
Configuring QoS
IGMP Snooping
When Internet Group Membership Protocol (IGMP) snooping is enabled on a switch, the switch
forwards multicast traffic only to those ports where the switch registers that multicast traffic as needed.
As a consequence, when a wireless client roams from one access point to another access point connected
to the same switch, the switch initially does not know whether or not the multicast traffic is needed on
the port to the second access point. The result is that the clients' multicast session is interrupted. IGMP
snooping on the access point helps mitigating this issue.
When the access points' IGMP snooping helper is enabled, and a client joins the access point cell, the
access point immediately sends a general IGMP query to the wireless LAN, prompting the client to send
in an IGMP membership report. The membership report is forwarded to the wired interface. When the
network infrastructure receives the host's IGMP membership report, it ensures delivery of that host's
multicast data stream to the access point port. The traffic is then relayed to the wireless interface. This
way, the wireless client multicast flow is not interrupted while roaming.
When Internet Group Membership Protocol (IGMP) snooping is enabled on a switch and a client roams
from one access point to another, the clients’ multicast session is dropped. When the access points’
IGMP snooping helper is enabled, the access point sends a general query to the wireless LAN, prompting
the client to send in an IGMP membership report. When the network infrastructure receives the host’s
IGMP membership report, it ensures delivery of that host’s multicast data stream.
The IGMP snooping helper is enabled by default. To disable it, browse to the QoS Policies - Advanced
page, select Disable, and click Apply.
Note If there is no multicast router for processing IGMP query and response from the host, it is mandatory
that no igmp snooping be configured on the access point. when IGMP snooping is enabled, all multicast
group traffic must send IGMP query and response packets. If IGMP query or response packets are not
detected, all multicast traffic for the group is dropped.
AVVID Priority Mapping
The 802.11e protocol assigns to voice packets a User Priority value of 6. Cisco wired networks follow
the IETF recommendation to assign to voice packets a class of service value of 5. Enabling AVVID
priority mapping maps the Ethernet packets tagged as class of service 5, to class of service 6 when these
packets are exchanged between the wireless and the wired sides of the access point. This feature enables
the access point to apply the correct priority to voice packets for compatibility with Cisco AVVID
networks.
AVVID priority mapping is enabled by default. To disable it, browse to the QoS Policies - Advanced
page, select No for Map Ethernet Packets with CoS 5 to CoS 6, and click Apply.
WiFi Multimedia (WMM)
Using the Admission Control check boxes, you can enable or disable WMM support on the access point's
radio interfaces. Default is enabled. When WMM is enabled, both WMM and non-WMM clients are
allowed to join the access point radio.
Note When you enable admission control (in RADIO1-802.11N2.4GHZ ACCESS CATEGORIES or
RADIO1-802.11N5GHZ ACCESS CATEGORIES), clients associated to the access point must complete
the WMM admission control procedure before they can use that access category.