I recently upgraded the Cisco WLC 5508 Controller Software from Version 7.4.100 to 7.6.130 and also the 'Field Recovery Image Version' image from verion 7.0 to 7.6. However, after the upgrde the status of the Mobility Anchor Group changed from 'UP' to 'Control Path Down' state.
Guest Anchor WLC Model: 2504
Guest Anchor WLC Software Version: 7.4
Guest Anchor Field Recovery Image Version : 7.0
Foreign WLC Model: 5508
Foreign WLC Software Version: 7.6
Foreign WLC Recovery Image Version : 7.6
Guest Anchor WLC is in DMZ and Foreighn WLC is internal to the network. There is firewall between both controller and the rules are configured to allow required ports.
Connect to both CLI on both WLC and tried 'mping' and 'eping' to test if we get any replies. The pings worked on for 'eping' which means the Data Path is UP and working between both controller . However there was no reply for 'mping' which means mobility group control path down.
The software upgrade was done on Foreign WLC so the initial thinking was that both WLC are on different version which can be reason as before the upgrade all was working OK. So upgraded the sofware on Guest Anchor to same version as on foreign.
Checked the firewall rules again but found no issue there with required ports still allowed through.
I went on to read the configuration manual (Manual) for Software Version 7.6 and started looking at configuration and requirements for 'Anchor Mobility'. The last requirement in the list was
In a guest anchor Cisco WLC deployment, ensure that the foreign Cisco WLC does not have a WLAN mapped to a VLAN that is associated with the guest anchor Cisco WLC.
I went back and look at the configuration of our WLCs and I could see on the forighn controller there was some legacy configuration for an interface which was no longer in use but the IP address Subnet used on that interface was the same subnet as that of the Management Interface on the Guest Anchor. I remove this interface configuration from foreighn WLC and soon after the mobility group status went to 'UP'
So this requirement was no there for version 7.4 but for sure is in version 7.6 and is enforced.