Flint 2 Ethernet Ports Stuck at 100 Mbps Negotiation – WiFi Fine, Tried Forcing Speeds via ethtool

Routers
1

Hi team,

I'm having an ongoing issue with my Flint 2 router where Ethernet ports are negotiating at 100 Mbps full duplex, capping my download speeds at ~93 Mbps down / 42 Mbps up, even though my Aussie Broadband NBN plan is 500/50 Mbps. WiFi (5 GHz) hits 332 Mbps down on my main PC and 280 Mbps on my Pixel 7 Pro, and direct to NBN box was 450 Mbps, so the line is fine. The problem is Ethernet-specific.Setup Details:

  • Router: GL.iNet Flint 2 (firmware 4.8.2)

  • PC Adapter: Realtek Gaming 2.5GbE Family Controller (latest driver 1167.15.1020.2024 from Realtek site)

  • Cable: 30m Cat 8 (Amazon link: https://www.amazon.com.au/dp/B086299XXB) – directly connected from Flint 2 LAN port to PC (bypassing Flint 1 AP).

  • VPN: ProtonVPN WireGuard on Flint 2 (MTU 1420), but speeds are same with VPN on/off.

  • OS: Windows 10 (version 10.0.19045.6332)

Symptoms:

  • Port Management shows WAN/LAN1 (and LAN5 when tested) at 100 Mbps full duplex.

  • ethtool verify on lan1/lan5 shows Speed: 100Mb/s, Duplex: Full, Auto-negotiation: on.

  • Tested with Pixel 7 Pro via USB-C Ethernet adapter – same 92 Mbps down.

  • WiFi to Flint 2 is fast (332 Mbps), so not NBN line or router overall.

What I've Tried:

  • Forced speed on PC adapter (Device Manager > Advanced > Speed & Duplex) to 1 Gbps and 2.5 Gbps Full Duplex – no change, still 100 Mbps.

  • Disabled Energy Efficient Ethernet, Green Ethernet, Flow Control, Large Send Offload, and Checksum Offload.

  • Forced speed via SSH on Flint 2 (ethtool -s lan1 speed 1000 duplex full autoneg off) – cut connection, but verify still shows 100 Mb/s after reboot.

  • 2.5 Gbps ethtool gave "invalid argument" error (as expected, since lan5 supports up to 1000 Mb/s).

  • Swapped to LAN5 – defaulted to 100 Mbps.

  • Cleaned ports, reseated cable – no change.

  • Power cycled NBN box and Flint 2.

  • Enabled Software/Hardware Flow Offloading – no change.

  • Reinstalled Realtek driver – no change.

ifconfig and ip link show outputs attached (from SSH).Is this a firmware bug in 4.8.2? Has anyone else seen 100 Mbps stuck negotiation on Flint 2? Suggestions for forcing 1 Gbps on lan1? Or is the 30m Cat 8 cable too long for reliable negotiation (even though it's rated for higher speeds)?Thanks for any help!

I feel I’ve tried everything.

2

Even though your Cat 8 cable is “rated” for 40G, 30m from Amazon is often the problem. Cheap Cat 7/8 patch cables are notorious for bad terminations and marginal pairs → auto-negotiation drops to 100 Mbps.

Try a short Cat 5e/6 cable (2–3m) directly between PC and Flint 2. If that links at 1 Gbps, you’ve found the culprit.

Cat 5e is good for 1 Gbps up to 100m, so you don’t need Cat 8.

2 Likes
3

I have the same problem: also tested with two flint2 and they still negotiate a 100mbps; I tried also to disable EEE on both lan1 without success;

The only way that I can found to have a stable 2.5gbps is to have a peer based on a RTL8125B

2 Likes
4

Can you please elaborate on that? or link to anything that does? :slight_smile:

5

If you take the LAN1 port of your flint2 and you attach it to a miniboard or a router that has a 2.5gbps port driven by a RTL8125B the flint2 is able to negotiate correctly the 2.5gbps speed.

But if I take 2 flint2 and I try to connect them through the LAN1 the only speed that I able to reach is 100mbps

1 Like
6

Going to try this :exploding_head::eyes:. I finally fixed my Ethernet stuck at 100Mbps with a decade-old SSD trick

7

Hi Team,

I’ve just bought a Flint 2 router and can’t get it to connect to my TPG NBN service. It shows as “Connecting” and then says “No cable detected.”

Here’s what I’ve tried so far:

  • Connected the WAN port on the Flint 2 to the NBN box using an Ethernet cable.

  • Restarted both the NBN box and the Flint 2.

Setup details:

  • TPG NBN

  • Flint 2 router

Before I start my own thread, I thought I’d ask here first—are there any quick fixes or settings I should check?

Thanks in advance!

10

For those interested in the issue that TPGNBN met, it is simply caused by a missing VLAN configuration.

See:

1 Like
11

How to and where to make that change? ;o

12

Sorry for the delayed response.

The issue reported by TPGNBN should not be related to your case. Their setup involved VLAN configuration on the WAN interface for ISP authentication, whereas your issue is that the link is negotiating at 100 Mbps.

To help narrow this down, could you please confirm the following:

  1. Have you tested with different Ethernet cables? If possible, try the cable included with the Flint 2 or a shorter cable that is known to work properly with other devices.
  2. If the issue persists, please try placing an unmanaged (dumb) switch between the Flint 2 and the ISP modem to see whether this changes the link speed.
  3. Please try configuring LAN 2 (the 1 Gbps port) as the WAN interface by following this tutorial, then connect it to your ISP modem and check whether the issue still occurs.
    GL-MT6000 (Flint2) How change LAN2 - LAN5 port to WAN - #28 by bruce
  4. When using the same Ethernet cable and modem port, do other devices negotiate at 1 Gbps normally?
13

hey my apologies for hijacking the thread but I’m facing exactly the same issue as OOP (my post: https://forum.gl-inet.com/t/flint-2-wan-lan-1-port-only-negotiating-10mbps-fd), I’ll just narrow down on the trouble shooting steps you shared

  1. Tested across 3 ethernet cables and 2 PCs with gigabit ports, all cables are giving me gigabit ethernet via my old router (tested via iperf and verified with link speed on windows (1000mbps/1000mbps)

  2. My original PC is connected to router via a network of dumb switches (2 dlink gigabit switches) and on my old router, I was easily getting gigabit, not on flint 2 and I only just swapped the routers out with no change in config, and further more, when I swapped in my old router back, I am again getting gigabit.

  3. not sure if its relevant in my case since all ports on the router are negotiating 100mpbs except for Lan 1 which is stuck on 10mbps FD

  4. No, tested across 2 laptops

    would really appreciate it if you can share any additional trouble shooting steps for this

14

Since you have already posted your own thread, we will discuss this issue there to avoid confusion.

1 Like