H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 20)

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and the subordinate AC acts as the backup AC. If the master AC fails, APs should quickly use the services
provided by the subordinate AC. A heartbeat mechanism is used between these two ACs, which ensures
that failure of the master will be detected quickly by the backup AC.
Figure 6 Dual link topology
In Figure 6 , AC 1 is working in master mode and providing services to AP 1, AP 2, AP 3 and AP 4. AC
2 is working in subordinate mode. APs are connected to AC 2 through subordinate tunnels. AC 1 and
AC 2 can be configured as backup for each other and start master/subordinate detection. When AC 2
detects AC 1 is down, AC 2 quickly converts the work mode from subordinate to master. All APs which
are connected to AC 2 through subordinate tunnels transform the tunnels to master tunnels and use AC
2 as the master AC. Once AC 1 is reachable again, it remains the backup.
Primary AC recovery
Figure 7 Primary AC recovery
In Figure 7 , AC 1 acting as the primary AC is the master (which has the connection priority of 7), and it
establishes an AC-AP tunnel connection with the AP; AC 2 acts as the subordinate AC. If AC 1 goes
down, AC 2 will act as the master until recovery of the AC-AP tunnel. This means once AC 1 is reachable
AC 2
AP 4 AP 1
AP 2 AP 3
AC 1
AC 1 AC 2
AP
Primary AC