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Aruba CX 6200M dropped TX packets on one port

(2026-07-21)

On an Aruba CX 6200M switch running AOS-CX, TX Drops (Transmitted Drops) almost always indicate egress port buffer congestion, rather than physical layer (Layer 1) cable damage. It means the switch successfully received the packet and wanted to send it out, but the egress queues for that specific port were entirely full.

  1. Identify the Exact Dropping QueueTo figure out what kind of traffic is being dropped

Run the following command to see which exact hardware queue (Q0 through Q7) is overflowing:

interface <member/slot/port> queues

eg:

IT-SW-L4-SVR-002# show int 1/1/1 queues
Interface 1/1/1 is up
 Admin state is up
               Tx Bytes        Tx Packets          Tx Drops
 Q0                   0                 0                 0
 Q1       1549366785240        1786420967            205993
 Q2                   0                 0                 0
 Q3                   0                 0                 0
 Q4                   0                 0                 0
 Q5                   0                 0                 0
 Q6                   0                 0                 0
 Q7            38316531            302593                 0

High-priority queues (Q5–Q7): If drops are happening here, critical real-time traffic (like voice or stack control) is backing up.

Low-priority queues (Q0–Q2): If drops are happening here, standard data (bulk file transfers, web browsing) is getting choked during brief bursts, which is standard.

  1. Common Root Causes & How to Fix Them

Speed Mismatch Microbursts (Most Common): If the data enters the switch on a 10Gbps uplink but is bound for a 1Gbps or 100Mbps endpoint, the traffic bursts will instantaneously overwhelm the slower port's buffer capacity.

Fix: Implement an aggressive QoS profile (apply qos schedule-profile) to protect mission-critical traffic, or bundle interfaces into a Link Aggregation Group (LAG) to add physical bandwidth.

An Oversubscribed Egress Port: The port is simply pushing more throughput than its maximum link speed allows over a prolonged period.

Fix: Check port utilization over time using show interface and verify if the data volume matches your expectations.

Legacy 10Mbps Speed Negotiation Bug: Certain AOS-CX versions suffer from an internal bug where any endpoint negotiating down to a legacy 10Mbps link speed (such as a device going into low-power sleep mode) falsely triggers thousands of TX drops per minute.

Fix: Update the switch to the latest AOS-CX stable release sequence to apply recent hardware-handling patches.

  1. Clear the Counters to Confirm Active Dropping

Ensure the drops are happening right now and are not historical relics from a past network event:

interface <member/slot/port> statistics

Use code with caution.Wait a few minutes and run show interface again. If the Tx Drops counter increments immediately on an idle or low-traffic link, check for a 10Mbps endpoint sleep bug.

(Source: Google Clanker)

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