AC66U slow with 6in4 - advise on new router

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Occasional Visitor
I've been struggling with my AC66U (old rev.) speed issues, finally I narrowed it down to IPv6. When I enable 6in4, my speed over ipv4 gets capped at around ~130-150 mbps, and router is lagging like crazy (ICMP 20-30ms, unresponsive web), as soon as I disable IPv6, I get ~700-900 mbps without problems.
Turns out IPv6 is not exactly the issue, but 6in4 tunnel disabling NAT acceleration is.
Original discussion about the issue is here.
I'm looking for advise on which router to get so that I can get 6in4 working with full gigabit speed? Is it ASUS only thing that NAT acceleration has to be off when using 6in4? Maybe I should look into other manufacturers then? I'm also using OpenVPN server, so a router that can handle that well is welcomed. Maybe even IPsec?


Very Senior Member
I use and recommend the RT-AC86U. I don't have any AX clients and use an asymmetrical 100 meg fiber connection. I do use a VPN server to access my LAN remotely and for security while on the road


Regular Contributor
it now depends on your budget - if it can can handle the rt-ax86u - go for that
if you just want the best cpu (and you'll want that for software nat) go for rt-ac86u
if you just want wifi6 (aka 802.11AX) go for rt-ax56u - cheapest
I don't think any of those can handle 1gbps with software nat only
if you're willing to get something else you can try Turris Omnia (should handle close to 1gbps with sw nat) or vilfo (

LE: the cheapest option could be Raspberry PI 4 + usb3-gigabit adapter and reuse your rt-ac66u as AP (I can provide details if you're interested)
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Occasional Visitor
Maybe there is a way to setup 6in4 on some other device on the network? I have rt-n16 in AP mode. Would it be possible to somehow setup 6in4 tunnel on it and advertise it to the network so it doesn't affect NAT acceleration on the main router? No idea why NAT acceleration has to be disabled with ipv6 tunnel though....
Through SSH maybe as running in AP mode disables functions as IPv6...

Edit: I've setup a tunnel on Windows 10 machine for now, and it's working as IPv6 gateway for the network :)
Though it's not on 24/7, so it's not ideal.
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