An enterprise is using wireless as the main network connectivity for clients.

When eping (EoIP ping) fails between two Cisco Wireless LAN Controllers, it indicates that the data path of the mobility tunnel is blocked. In Cisco AireOS wireless networks, the mobility data path uses IP Protocol 97 (EtherIP — Ethernet-over-IP encapsulation) for tunneling client traffic between the anchor and foreign controllers. This is distinct from the control path, which uses UDP port 16666. When the mobility data path (IP Protocol 97) is blocked by a firewall or ACL between the two controllers ' networks, eping will fail because eping specifically tests the EoIP data encapsulation path. After a power cut, when clients disconnect and attempt to roam between APs on different controllers, the mobility tunnel must be operational for session continuity. If IP Protocol 97 is blocked, the mobility data plane cannot function, causing client disconnections during inter-controller roaming events. The other IP protocols listed (67, 77, 87) are not used for Cisco WLC mobility tunneling. Reference: WLSD Study Guide — Mobility Tunnel Data Path, IP Protocol 97 (EtherIP), eping Command and Troubleshooting.