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300-425 · Question #211

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…

The correct answer is A. For the same SSIDs, use the same VLAN IDs and subnets on both WLCs. During AireOS to IOS XE migration, seamless Layer 3 roaming requires that the same SSIDs use identical VLAN IDs and subnets on both controllers so clients retain their IP addresses when roaming.

Mobility

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?

Options

  • AFor the same SSIDs, use the same VLAN IDs and subnets on both WLCs.
  • BFor different SSIDs, use different VLAN IDs and subnets on both WLCs.
  • CFor different SSIDs, use the same VLAN IDs and subnets on both WLCs.
  • DFor the same SSIDs, use different VLAN IDs and subnets on both WLCs.

How the community answered

(20 responses)
  • A
    75% (15)
  • B
    15% (3)
  • C
    5% (1)
  • D
    5% (1)

Why each option

During AireOS to IOS XE migration, seamless Layer 3 roaming requires that the same SSIDs use identical VLAN IDs and subnets on both controllers so clients retain their IP addresses when roaming.

AFor the same SSIDs, use the same VLAN IDs and subnets on both WLCs.Correct

When the same SSID is configured with the same VLAN ID and subnet on both the AireOS and IOS XE WLC, a roaming client retains its IP address and session continuity across controllers. This subnet consistency is the core requirement for seamless Layer 3 roaming in a mixed-controller mobility group - it eliminates the need for re-authentication or IP renewal during handoff.

BFor different SSIDs, use different VLAN IDs and subnets on both WLCs.

Different SSIDs with different VLANs and subnets place clients on entirely separate networks, making inter-controller roaming impossible since clients would have no common network context.

CFor different SSIDs, use the same VLAN IDs and subnets on both WLCs.

Different SSIDs cannot be part of the same roaming domain even if they share VLANs, because roaming is tied to matching SSID identifiers and the client association context.

DFor the same SSIDs, use different VLAN IDs and subnets on both WLCs.

Using different VLAN IDs and subnets for the same SSID across WLCs forces clients to obtain a new IP address when roaming, breaking session continuity and making Layer 3 roaming non-seamless.

Concept tested: Inter-controller Layer 3 roaming during AireOS to IOS XE migration

Source: https://www.cisco.com/c/en/us/td/docs/wireless/controller/9800/config-guide/b_wl_16_10_cg/mobility.html

Topics

#AireOS IOS XE migration#mobility group#Layer 3 roaming#VLAN configuration

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