Exam 300-425 topic 1 question 59 discussion

An enterprise is using the wireless network as the main network connection for corporate users and guests. To ensure wireless network availability, two standalone controllers are installed in the head office. APs are connected to the controllers using a round-robin approach to load balance the traffic. After a power cut, the wireless clients disconnect while roaming. An engineer tried eping from the controller but fails. Which protocol needs to be allowed between the networks that the controllers are installed?