GT-BE98 10G Gaming Port limits WAN upload to ~1 Gbps, while 2.5G LAN reaches full 2 Gbps upload

[Sundraw]

Hi everyone,

I’m trying to understand whether this is a firmware issue, hardware limitation, or compatibility problem involving the 10G Gaming port on my ASUS GT-BE98.

My internet line is 10 Gbps down / 2 Gbps up.

Setup
- Router: ASUS GT-BE98
- Tested firmware: latest official ASUS firmware, Gnuton 3006.102.6_1-gnuton1
- Mode: Wireless Router
- ONT: external ONT
- Motherboard: Z790
- CPU: Intel i7-14700K
- Tested NICs: Realtek RTL8127, Realtek RTL8125 (5 GbE)
- Ethernet cable: tested and working

Problem
If the PC is connected to the 10G Gaming port, WAN upload is limited to about 1 Gbps.
If I move the exact same PC / same cable / same NIC to a 2.5G LAN port, WAN upload goes up to the expected ~2 Gbps.

So the issue appears to be specific to the 10G Gaming port.

What I tested
I tested this with both RTL8127 and RTL8125, on Windows 11 and Linux.

On both NICs I disabled the usual troubleshooting settings:
- Flow Control
- Energy Efficient Ethernet / EEE
- Interrupt Moderation
- other commonly disabled advanced NIC options where applicable

The result is always the same:
- 10G Gaming port -> ~1 Gbps upload
- 2.5G LAN port -> ~2 Gbps upload

So this is reproducible across:
- two different Realtek NICs
- two different operating systems
- same PC
- same cable
- same WAN line

Router settings
- Adaptive QoS: disabled
- Game Boost: disabled
- Gaming Port Priority: disabled
- Open NAT / port forwarding: enabled, but I assume unrelated to raw WAN throughput
- Under LAN > Switch Control:
- Jumbo Frame: disabled
- Bonding / Link Aggregation: disabled
AiProtection / Traffic Analyzer / VPN / Parental Controls are also disabled

There is no visible NAT acceleration toggle in this firmware.

Important additional point
The issue happens on both:
- latest official ASUS firmware
- Gnuton 3006.102.6_1-gnuton1

So this does not look limited to a single firmware build.

Why I suspect the router
At this point, the only variable that changes the result is the router port:
- 10G Gaming port -> ~1 Gbps upload
- 2.5G LAN port -> ~2 Gbps upload

Everything else stays the same:
- PC
- cable
- WAN line
- NIC family
- OS

That makes me suspect either:
- a GT-BE98 10G port / switch path issue
- a 10G PHY compatibility issue
- some router-side limitation affecting WAN upload only

Questions
- Has anyone seen similar behavior on the GT-BE98 or BE98 Pro 10G ports?
- Could this be related to the internal switching / routing path of the 10G Gaming port?
- Has anyone compared WAN upload on the 10G Gaming port vs 2.5G LAN?
- Could this still be a PHY compatibility issue even though it happens with both RTL8127 and RTL8125?
- Would testing with an Intel X550-T1 or Marvell/Aquantia AQC113-based NIC be worthwhile, or does this look clearly router-side?

My goal is to get the full 2 Gbps upload from my 10/2 line while using the 10G LAN port.

Any suggestions for additional tests are welcome. Thanks.

 

[degrub]

What is the link rate detected/negotiated by the ASUS and PC while plugged into the 10 Gbit/s port ?

If you use the 10Gb REALTEK nic, what is the link rate negotiated between the PC and the ASUS 10Gb port ?
If it doesn't sync at 10Gb/s something is physically wrong or drivers.

2.5 Gb is an oddball for compatibility. You may be able to place a non managed 10 Gb switch between the two and solve the issue.

 

[Sundraw]

The link is correctly negotiated at 10/10 Gbps (RX/TX), so this does not appear to be a simple physical link or cabling issue.
I also tested with another ASUS router (BQ16) on its 10G WAN/LAN ports and I see the same behavior: WAN upload stays around 1.1-1.2 Gbps.
Example result while link is negotiated at 10/10 Gbps:
- Download: ~7079 Mbps
- Upload: ~1190 Mbps

So at this point the problem seems to be real throughput on ASUS 10G ports, not link negotiation.

 

[fryedchikin]

Not seeing this issue with a GT-BE98 Pro. I can easily cap out my 5 Gig symmetrical connection using a TP-Link TX401 NIC.

 

[Sundraw]

Quick update.
Given the suggestions and after testing two different Realtek NICs (RTL8127 and RTL8125) with the same result (~1.1–1.2 Gbps WAN upload on the ASUS 10G port), I decided to order a TP-Link TX401 (Marvell/Aquantia based NIC).
It should arrive tomorrow and I will test it directly connected to the 10G LAN port on the router.
If the upload goes up to ~2 Gbps (which is my line limit), that would strongly suggest the issue is related to the Realtek NICs interacting with the ASUS 10G port.
I'll report back with results once I install and test the TX401.
For reference, link negotiation is already confirmed at 10/10 Gbps and the issue persists across two ASUS routers (GT-BE98 and BQ16), two cables and both Windows and Linux.