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Difficulty: HardAP and WLC Management Access Connections

A network administrator is deploying a Cisco Lightweight Access Point (AP) connected to a Layer 2 switch port configured as an 802.1Q trunk. The AP is intended to exchange CAPWAP control messages with the Wireless LAN Controller (WLC) management interface over the native VLAN while carrying client traffic on tagged VLANs. Switch syslogs immediately report a 'Native VLAN mismatch' notification on the interface, and the AP fails to join the controller. Which condition explains why management access between the AP and the WLC is failing?

  1. Untagged CAPWAP discovery and management packets sent by the AP arrive on a mismatched native VLAN at the switch, placing management traffic into an unintended VLAN segment.Answer
  2. B
    Enabling PortFast on the switch port automatically revokes trunking capabilities, preventing tagged client traffic and untagged management traffic from reaching the WLC.
  3. C
    Lightweight APs strictly reject untagged frames on trunk interfaces and mandate that management CAPWAP traffic carry an explicit 802.1Q VLAN tag for VLAN 1.
  4. D
    CDP detects the neighbor interface architecture mismatch and forces the switch port into an err-disabled state to prevent CAPWAP control plane corruption.

Answer

Untagged CAPWAP discovery and management packets sent by the AP arrive on a mismatched native VLAN at the switch, placing management traffic into an unintended VLAN segment.
Cisco Lightweight Access Points transmit their initial CAPWAP discovery and management control traffic as untagged frames by default. When connected to an 802.1Q trunk port, these untagged frames are mapped directly to the switch port's native VLAN. A native VLAN mismatch causes the switch to place the AP's management frames into an incorrect VLAN segment, preventing IP communication with the Wireless LAN Controller (WLC) management interface.

Step-by-Step Solution

1
Identify the transmission mode of AP management and CAPWAP control traffic on an 802.1Q trunk port.
By default, Cisco Lightweight Access Points transmit CAPWAP management packets as untagged frames.
The AP relies on the native VLAN of the connected switchport to process untagged management traffic.
2
Analyze the impact of a Native VLAN mismatch on untagged frames.
When a switch port's native VLAN does not match the configured subnet or opposing link expectation, untagged packets are forwarded onto the incorrect VLAN.
Layer 2 switches assign incoming untagged frames to the port's configured native VLAN.
3
Determine the effect on WLC management access and CAPWAP tunnel establishment.
Because the AP management frames enter the wrong VLAN/IP subnet, IP routing to the WLC management IP fails and the CAPWAP state machine cannot complete.
CAPWAP discovery and join requests require bidirectional IP connectivity between the AP management IP and the WLC management interface IP.

Key Concept

AP and WLC Management Access over 802.1Q Native VLANs
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Topics

AP and WLC Management Access Connections

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