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Table Of Contents
response packet is not multicast. The exiting users get to know about the new user only after they send a
periodic query.
mDNS multicast response propagation allows services to multicast the response packet. This allows the
existing users to instantly see a new user when a new user logs in.
The mDNS response packet for iChat or Messages Application is multicast across all VLANs that are trunked in
the controller except:
l If the VLAN is globally disallowed.
l If the iChat service is disallowed for a VLAN.
In both scenarios, the mDNS response message is not propagated and:
l mDNS queries for iChat records from a disallowed VLAN are dropped.
l mDNS responses are not propagated to a disallowed VLAN.
l When an allowed VLAN is disallowed, users disappear from the buddy list of other users when they query
for the service next time. This may take a maximum of one hour.
l When a disallowed VLAN is allowed, wildcard queries are sent to all users for discovery.
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 controller models:
Controller Model Number of mDNS Servers
W-7240 10000
W-7220 7000
W-7210 5000
W-7205 2000
W-7030 1000
Table 244: Controller model and number of supported mDNS servers
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