Device Information
- Model: GL-BE9300 (Flint 3)
- Firmware: 4.8.99 (Beta)
- Issue: RTL8372 Switch - Link Instability / Auto-Negotiation Problems
Problem Summary
Multiple LAN ports experience link instability issues:
| Port | Connected Device | Expected Speed | Problem |
|---|---|---|---|
| lan1 | Linux PC (RTL8125 2.5GbE) | 2500 Mbit/s | Auto-negotiation starts at 100Mbit, then re-negotiates |
| lan2 | Xbox Series X | 1000 Mbit/s | Severe link flapping (connection drops every few minutes) |
| lan3 | Smart TV | 100 Mbit/s | Frequent disconnects/reconnects |
Detailed Symptoms
lan1 - Auto-Negotiation Failure (2.5G Port)
Symptom: When connecting a 2.5GbE device, the link always starts at 100Mbit, goes down after ~18 seconds, then re-negotiates correctly at 2500Mbit.
Evidence from dmesg:
[1506591.157186] rtl8372-mdio 90000.mdio:1d: lan1 link up, speed 100
[1506609.876788] rtl8372-mdio 90000.mdio:1d: lan1 link down
[1506615.076795] rtl8372-mdio 90000.mdio:1d: lan1 link up, speed 2500
Root Cause Found: Energy Efficient Ethernet (EEE) mismatch between client and Flint 3.
Workaround: Disabling EEE on the client fixes this issue:
# On Linux client
sudo ethtool --set-eee enp7s0 eee off
After disabling EEE, the link negotiates directly at 2500Mbit:
[1534689.767596] rtl8372-mdio 90000.mdio:1d: lan1 link up, speed 2500
[1534832.246977] rtl8372-mdio 90000.mdio:1d: lan1 link down # cable unplugged
[1534840.567031] rtl8372-mdio 90000.mdio:1d: lan1 link up, speed 2500
Note: The Flint 3 does not advertise EEE support to link partners:
Link partner advertised EEE link modes: Not reported
This causes negotiation problems with EEE-enabled clients.
lan2 - Link Flapping (Xbox)
Symptom: Xbox connection drops every few minutes, making online gaming impossible.
Evidence from dmesg:
[1504284.444683] rtl8372-mdio 90000.mdio:1d: lan2 link up, speed 1000
[1504290.684589] rtl8372-mdio 90000.mdio:1d: lan2 link down # 6 seconds later
[1504293.804593] rtl8372-mdio 90000.mdio:1d: lan2 link up, speed 1000
[1504549.643736] rtl8372-mdio 90000.mdio:1d: lan2 link down # 4 minutes later
Workaround: None found. Rebooting the router temporarily helps but problem recurs.
lan3 - Frequent Reconnects (TV)
Symptom: Smart TV frequently loses connection and reconnects.
Evidence from dmesg:
[1532471.455288] rtl8372-mdio 90000.mdio:1d: lan3 link down
[1532474.575593] rtl8372-mdio 90000.mdio:1d: lan3 link up, speed 100
What I Tested
Different Ethernet cables (Cat6) - problem persists- Different devices on same ports - problem persists
- Router reboot - temporarily fixes, then recurs
- Disabled EEE on Linux client - fixes lan1 issue
lan2 and lan3 still have issues regardless of above
Monitoring Setup
I have monitoring scripts running to capture link events:
eth_monitor.sh (runs every 5 minutes via cron):
#!/bin/sh
LOGFILE="/root/eth_debug.log"
TS=$(date "+%Y-%m-%d %H:%M:%S")
echo "=== $TS ===" >> $LOGFILE
echo "[LINK]" >> $LOGFILE
swconfig dev switch0 show 2>/dev/null | grep -E "Port |link:" >> $LOGFILE
echo "[TEMP] $(cat /sys/class/thermal/thermal_zone*/temp | tr '\n' ' ')" >> $LOGFILE
echo "[LOAD] $(cat /proc/loadavg)" >> $LOGFILE
echo "[MEM] $(free | grep Mem | awk '{print $3"/"$2}')" >> $LOGFILE
dmesg | grep "rtl8372" | tail -3 >> $LOGFILE
echo "" >> $LOGFILE
Feature Request
Please consider:
- Adding EEE configuration option in the web interface to enable/disable EEE per port
- Investigating RTL8372 driver stability for lan2/lan3 link flapping
- Improving auto-negotiation behavior for 2.5GbE connections
System Information
Firmware: 4.8.99 (Beta)
Switch Chip: RTL8372
Driver: rtl8372-mdio
Port Status (swconfig):
- Port 0: link:up speed:10000baseT full-duplex (internal)
- Port 1: link:up speed:10000baseT full-duplex (internal)
- Port 2: link:down
Full debug logs available upon request