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Difficulty: MediumWLAN Infrastructure Connections and LAG

A network administrator is establishing link aggregation between a Cisco AireOS Wireless LAN Controller (WLC) and an upstream Cisco Catalyst switch to increase bandwidth and provide interface redundancy. The administrator configures ports GigabitEthernet 1/0/1 through 1/0/4 on the Catalyst switch using the command 'channel-group 10 mode active' and enables LAG on the WLC. However, after the WLC reboots, the EtherChannel fails to negotiate successfully. Which condition is causing this link aggregation failure?

  1. The upstream switch ports are configured for dynamic LACP negotiation, but Cisco AireOS WLCs only support static EtherChannel bundles configured with mode on.Answer
  2. B
    The distribution ports on the WLC are operating in Local mode, which disables link aggregation until connected access points are converted to FlexConnect mode.
  3. C
    The switch port channel interface contains a native VLAN mismatch because dynamic trunk negotiation requires management traffic to strictly use VLAN 1.
  4. D
    Cisco Discovery Protocol (CDP) TLV messages are being dropped across the port channel, causing the WLC to reject LACP control frames from the switch.

Answer

The upstream switch ports are configured for dynamic LACP negotiation, but Cisco AireOS WLCs only support static EtherChannel bundles configured with mode on.
Cisco AireOS Wireless LAN Controllers require all connected distribution system ports to be bundled into a single static EtherChannel. Because AireOS does not support LACP (IEEE 802.3ad) or PAgP negotiation protocols, the upstream switch interfaces must be configured with 'mode on'. When the switch ports are configured with 'mode active', the switch expects LACP packets that the AireOS controller never sends, preventing the link aggregation bundle from establishing.

Step-by-Step Solution

1
Identify the protocol support for Link Aggregation (LAG) on Cisco AireOS Wireless LAN Controllers.
AireOS controllers do not support dynamic EtherChannel negotiation protocols such as LACP or PAgP.
LAG on AireOS bundles all physical distribution system ports into a single logical channel that requires unconditional static bundling on the connected switch.
2
Evaluate the switch port configuration command 'channel-group 10 mode active'.
The 'mode active' keyword enables LACP dynamic negotiation on the Catalyst switch ports.
Because the WLC will not transmit or respond to LACP control packets, the switch ports remain in an unbundled or suspended state waiting for LACP negotiation.
3
Determine the necessary configuration change on the switch interfaces.
Change the switch port channel command to 'channel-group 10 mode on'.
Configuring 'mode on' forces the switch ports into a static EtherChannel without attempting LACP or PAgP negotiation, matching the WLC requirements.

Key Concept

Cisco AireOS WLC Link Aggregation (LAG) EtherChannel Mode Requirements
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Topics

WLAN Infrastructure Connections and LAG

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