The AirGroup cache is updated with iChat records thus ensuring that the cache of the existing users is also
updated. CPPM/CLI policies are not applied to iChat records because the mDNS response is multicast. The
mDNS response messages are multicast whenever the status of a user changes and similar messages are also
multicast.
The response for mDNS iChat queries is L2 unicast back to the sender from the AirGroup cache while the
mDNS response packets are L3 multicast.
When the iChat service is disabled from enabled state, new messages are neither propagated nor responded
until they query for the service again. After an hour, the existing users disappear because query and responses
are not honored. When the iChat service is enabled, discovery packets are sent to determine all iChat users.
The performance of an iChat server is not the same as the performance of an AirGroup server. The number of iChat
servers supported is less than the number of AirGroup servers supported.
Maximum Number of iChat Users
The maximum number of iChat users is limited to 2000. Each iChat user is an mDNS server and their
announcement messages are L2 multicast. The following table lists the number of mDNS servers supported in
different switch models:
Switch Model Number of mDNS Servers
OAW-4750 10000
OAW-4650 7000
OAW-4550 5000
OAW-4450 2000
OAW-4030 1000
OAW-4024 600
OAW-4010 500
OAW-4005 300
Table 255: Switch model and number of supported mDNS servers
In a multi-switch deployment with AirGroup solution:
n The local switch sends the response from an mDNS device for iChat service to other switches in the cluster.
This is in addition to local switch performing L2 multicast of the message to all VLANs.
n The corresponding switch multicasts the message to all the VLANs that are trunked in it.
n When a user moves from one switch to another switch, two user entries exist in the user cache for the same
user until the user entry is deleted from the first switch. The two user entries exist because the IP address,
which is part of the mDNS payload, changes when a user moves from one switch to another switch. If IP
mobility is enabled, only one user entry exists because the user retains the IP address across the switches.
Configuring mDNS Multicast Response Propagation
Use the following procedures to enable or disable mDNS multicast response propagation:
In the WebUI
To enable iChat using the switch WebUI:
AOS-W 6.5.3.x | User Guide AirGroup | 1034
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