Does Cisco 3504 Wireless LAN controller have HA (High Availability) option ?

Many previous Cisco wilress LAN controller like 5508, 5520, 2504 have the HA SKU unit, which could be used for N+1 HA (or clustering on the 5508) without additional license fees – the HA unit supported the maximum amount of APs for 90 days. But datasheet of Cisco 3504 WLC does not show clearly on the HA availability.

Does Cisco 3504 Wireless LAN controller (AIR-CT3504-K9) have HA(High Availability) option ?

The answer is ‘YES’. The 3504 WLC supports high availability (Client SSO + AP SSO), it also supports N+1 High Availability. It’s basically what we are used to in other WLCs, like the 5508 or 5520, one becomes the Active and the other becomes the Hot Standby, synchronization occurs through the Redundancy Port. In terms of licensing, these controllers support Smart Licensing or RTU licensing.

How does it work ?

High Availability is for box-to-box redundancy. In other words, 1:1 where one WLC will be in an Active state and the second WLC will be in a Hot Standby state continuously monitoring the health of the Active WLC via a Redundant Port. Both the WLCs will share the same set of configurations including the IP address of the Management interface. The WLC in the Standby state does not need to be configured independently as the entire configuration (Bulk Configuration while boot up and Incremental Configuration in runtime) will be synced from the Active WLC to the Standby WLC via a Redundant Port. The AP’s CAPWAP State (only APs which are in a run state) is also synced, and a mirror copy of the AP database is maintained on the Standby WLC. The APs do not go into the Discovery state when the Active WLC fails and the Standby WLC takes over the network’s Active WLC.

There is no preempt functionality. When the previous Active WLC comes back, it will not take the role of the Active WLC, but will negotiate its state with the current Active WLC and transition to a Standby state.

Like on other WLC, WLC 3504 supports both AP SSO and Client SSO. Given below is how one would connect two WLC 3504 using the RP port(back to Back) in HA Setup.

*Note*: One can also connect RP port through a L2 switch.

To connect a pair of WLC 3504 in HA Setup to the wired network, one can use the following deployment examples. Please note that only two links are shown from WLC3504 to the switch(s) but one can connect all four of the GE links + mGig link for LAG.