An engineer must configure the virtual IP address on multiple controllers in a mobility group.

In a Cisco wireless mobility group, all Wireless LAN Controllers (WLCs) must be configured with the same virtual IP address to ensure proper roaming. The virtual IP address is a Layer 3 construct used by wireless clients during the DHCP renewal process when roaming between subnets managed by different WLCs. All WLCs in the same mobility group use the same virtual IP (typically from the unused 1.1.1.0/24 or similar non-routable space) so that clients receive consistent DHCP server responses regardless of which controller they are associated with. If different virtual IP addresses were used (Option B), clients roaming between controllers would experience DHCP failures during inter-controller roaming because the DHCP server address seen by the client would change. Options A and C relate to DNS hostname configuration, which is useful for AP discovery but does not affect the roaming behavior of client devices. The virtual IP address consistency across all mobility group members is a fundamental requirement for seamless inter-controller roaming. Reference: WLSD Study Guide — Mobility Group Configuration, Virtual IP Address, Inter-Controller Roaming Requirements.