Random Reboots on Cambium XV2-21X AP
Overview: This document outlines a field observation regarding unexpected reboots of a Cambium XV2-21X Access Point (AP) post-deployment. The issue was traced to power negotiation conflicts between the AP and the Cisco PoE switch, leading to port resets and subsequent AP restarts. This document provides a detailed account of the scenario, root cause, and resolution steps from a Cambium AP perspective.
Deployment Detail:
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Access Point Model: Cambium XV2-21X
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Firmware Version: 6.6.2.1
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PoE Switch: Cisco CBS350-24P
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Switch Firmware Version: 3.0.0.69
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PoE Negotiated Power (Port Level): 12.9W
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Overall Switch Power Load: < 60%
The AP was powered via PoE using a Cisco CBS350-24P switch. The AP’s radio transmit power was set to AUTO, which resulted in dynamic adjustment of transmit levels depending on environmental conditions and client density.
Problem Description: During peak usage or when multiple clients with weak signal strength attempted to associate, the AP likely required more than the negotiated 12.9W. This exceeded the power threshold and triggered port protection on the Cisco switch, which momentarily shut down and re-enabled the port. This caused the AP to reboot unexpectedly.
Root Cause Analysis:
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LLDP-Based Power Negotiation Conflict: The AP and switch were negotiating power dynamically using LLDP (Link Layer Discovery Protocol). Under certain conditions, this negotiation failed to provide adequate power.
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Auto Transmit Power Adjustment: High transmit power levels, especially at level 27, increased power draw.
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Cisco Switch Port Protection Behavior: On detecting overdraw, the switch reset the port for protection.
Resolution Steps:
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Disable LLDP Power Requests on Cambium AP to eliminate reliance on dynamic power negotiation:
no lldp request-power -
Manually Increase PoE Power Limit on Cisco Switch to ensure sufficient power is available to the AP. The power is specified in millwatts:
interface gigabitethernet0/1 power inline limit 30000This ensures the port can supply power levels required under high client load and transmit power conditions.
Post-implementation of the above configurations, the Cambium XV2-21X AP has remained stable with no further reboots observed. The issue was conclusively identified as a power negotiation and supply limitation, which was mitigated through disabling LLDP-based power requests and statically assigning a higher power limit on the switch port.