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.

1 Like
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