In a converged access deployment with two Cisco Catalyst 3850 stacks, each operating as MC/MA, when a client attempts to roam between the Cisco Catalyst 3850 stacks, roaming fails. When some clients…

When different client subnets are configured on the same WLAN across the two 3850 stacks, a roaming client moves from one subnet to another, forcing a Layer 3 roam that results in the client obtaining a new IP address from the DHCP scope of the new stack. This breaks session continuity for clients that cannot handle the IP change gracefully.

Cisco Compatible Extension version compatibility affects features like fast roaming and voice metrics but does not cause IP address changes or disassociation during inter-stack roaming.

Configuring the same VLAN number on the WLAN of both 3850 stacks in a converged access MC/MA topology causes a VLAN conflict because the mobility architecture requires unique VLAN mappings per MA to correctly build mobility tunnels. This conflict leads to clients either failing to re-associate or experiencing extended delays during the roam.

Different Bridge Group IDs would cause issues, but identical Bridge Group IDs on both stacks are actually required for proper mobility group operation and are not the cause of the described roaming failures.

Configuring the same client subnet on both stacks is the correct design for seamless Layer 2 roaming, allowing clients to retain their IP address and roam without disruption.