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AX86u & GT-AX6000 2.5gb LAN speed issue

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Hey all,

I’ve been testing out an AX86u and GT-AX6000 and am having a weird issue with LAN speed.

internet connection: 1200/200 Xfinity


Xfinity XB8 modem/router, in bridge mode (needed for 200 upload on xfinity unfortunately)

AX86u, latest Merlin installed
GT-AX6000, latest Merlin installed

both routers have been factory reset (with initialize setting checked) and all settings that could effect speed/hardware acceleration combed through


There seems to be an issue with 1gb/1gb LAN speed. When using 2.5gb WAN

When both routers are hooked up (at separate times for testing) to the modem via 2.5gb, wired LAN devices aren’t receiving full line speed. 600-800mbps typically.

both the routers report the correct DL speed (between 1200/1400mbps) on the router level speed test in the QOS section. I also have a 2.5gb port on my PC that gets me the full 1400 speed on a variety of different speed tests (GT-AX6000).

When I switch the AX86u to 1gb WAN, line speed on all LAN devices get the expected 920-940mbps rate.

While I can’t switch off the 2.5gb WAN port on the GT-AX6000, the XB8 modem has multiple ports that are also 1gb. When switching to one of those, the speed gets better. 850-900ish range. But not the expected performance like the AX86u. This doesn't appear to be the case anymore. Getting line speed in this configuration after further testing.

Other troubleshooting steps involved swapping out multiple certified CAT 5E cables and a CAT 6. Power cycling all devices. I had a multi gig Netgear modem previously and think the like rate may have been fine when the GT-AX6000 was on 2.5gb but I can’t really remember.

Looking for any advice, as this seems to be a pretty peculiar issue. Been a long time lurker so it’s fun to post something for once!
Last edited:
Question/clarifiication ; So you have the 2.5 port (wan) on AX6000 and/or the 2.5 port on the AX86 plugged into the modem's 2.5.. then you plug your PC with the 2.5 NIC (assume its a fast PC) into a 1GB LAN port.. are you getting 900+ or only 600-800 ?
Yup, only getting 600-800 in that scenario. PC has intel10900K, 32gb 3600mhz ram, 3090, Samsung pro SSD etc.

Other LAN device is laptop with i7, 32gb ram, etc. Same behavior. 940mb line speed with the ax86u in 1g wan. 600-800 when 2.5G (modem) -> 2.5G (router) -> 1G (laptop).
It seems odd..why would the Wan negotiated speed effect the Lan. And you say it happen with both the ax6000 and ax86u? Maybe someone with a 2.5Gbit modem connected to one of these could say what their Lan speeds are.
Yup, very perplexing. One thing I didn’t think to look at was cpu load. Because it seems similar to the behavior seen when running sqm cake or something like that. Will check the cores when I get home tonight.

happens with both routers in 2.5G WAN

Would be great if someone with a 2.5g Xfinity modem in bridge mode and a similar router could chime in on their performance lol.
I have Frontier 2.5g service..my Frontier ONT is connected to the 2.5g wan port on my GTAX-6000..My Mac pro EN-0 1gb is connected to the 6000's 2.5g Lan port..Using the Qos Speed test, the down side is 2345, the upside is 980.. thats pretty close to correct for a 2.5/1.2 fiber service...using ookla speed test app for the Mac, with a 1g ethernet connected to the Lan 2.5 port, I get 940 down, 940 up, which is about all it will do, with overhead ...when I had 1g/1g service, the mac would get 800/800, due to other things streaming and using some of the bandwidth, is my guess...

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