Seamless Layer 3 Roaming Configuration

300-425 By islever Editorial Last updated

Optimize client roaming Design mobility groups based on mobility roles

Short answer

D For the same SSIDs, use different VLAN IDs and subnets on both WLCs to enable Layer 3 roaming.

Question

A customer currently is migrating the old wireless infrastructure to a new Cisco IOS XE-based solution and wants a mobility group configured between a Cisco AireOS WLC and an IOS XE WLC. During the migration phase from AireOS to IOS XE, the Layer 3 roaming between the WLCs must be seamless. Which action meets the requirements?
  1. For the same SSIDs, use the same VLAN IDs and subnets on both WLCs.
  2. For different SSIDs, use different VLAN IDs and subnets on both WLCs.
  3. For different SSIDs, use the same VLAN IDs and subnets on both WLCs.
  4. For the same SSIDs, use different VLAN IDs and subnets on both WLCs. Correct Answer

Key Takeaways

Layer 3 inter-controller roaming requires the same SSID to allow seamless client transition, but different VLANs and subnets to trigger the Layer 3 mobility tunnel.

Seamless Layer 3 roaming between Cisco WLCs requires clients to maintain their wireless connection across different subnets. This page establishes that for Layer 3 roaming to occur, the SSIDs must be identical while the VLANs and subnets must differ.

Common mistake: Choosing option A because it seems intuitive for seamless roaming, but using the same VLAN IDs and subnets results in Layer 2 roaming, not Layer 3.

Expert Analysis

Why the Answer Is Correct

For seamless inter-controller roaming, the client must associate to the same SSID on both wireless LAN controllers; otherwise, the client would disconnect and reassociate rather than roam. Because the requirement specifies Layer 3 roaming, the client must move to a different subnet on the foreign controller, which necessitates different VLAN IDs and subnets. Option D correctly identifies this combination of same SSIDs with different VLANs and subnets.

Why the Other Options Are Wrong

Option A describes Layer 2 roaming, where the client stays in the same subnet across both controllers, contradicting the Layer 3 requirement. Options B and C suggest using different SSIDs, which prevents seamless roaming entirely because the client would see them as distinct networks and drop its connection before reassociating. Option C also incorrectly suggests using the same VLANs and subnets, which would force Layer 2 roaming.

Community Comment Notes

The community correctly emphasizes that the distinction hinges on the Layer 3 requirement, noting that "if the same VLAN and subnet then it is not Layer 3 roaming". Another user pointed out that different SSIDs eliminate roaming altogether, stating "If different SSID then there's no roaming at all". The consensus highlights that Layer 3 roaming inherently requires different subnets.

Official Reference

https://www.cisco.com/c/en/us/td/docs/wireless/controller/8-5/config-guide/b_cg85/mobility_groups.html

This link opens the official vendor documentation in a new tab.

Exam Strategy

When analyzing roaming questions, first determine if the roaming is Layer 2 or Layer 3. Layer 2 roaming uses the same subnet and VLAN, while Layer 3 roaming requires different subnets. Always remember that seamless roaming fundamentally requires the same SSID; different SSIDs force a full reassociation.

Community Votes

D
100%

100% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 5 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 5

  1. Lakshan__97 👍 3 Answered D
    it should be D, Answer A says Inter controller LAyer 2 .
  2. Jonycici 👍 2 Answered D
    I believe the key word here is Layer 3. It they are roaming in Layer 3, each WLC will be in a different subnet
  3. a8cb452 👍 1 Answered D
    It has to be D. If different SSID then there's no roaming at all. If the same VLAN and subnet then it is not Layer 3 roaming (it's layer 2 roaming).
  4. Farhad123 👍 1
    A is correct , same SSID should be used and to have seamless layer 3 roaming we should use the same VLAN IDs and subnets on both WLCs.
  5. Farhad123 👍 1 Answered D
    Need to correct my previous answer , since the question is saying Layer 3 roaming, then the VLAN id and subnet should be different

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