topic Re: MAP-T IPv4 speeds in Broadband

MAP-T IPv4 speeds

WhiskerP — Mon, 20 Apr 2026 13:30:13 GMT

Hi, I've recently had 500mbps broadband installed and provided the other side is on native IPv6 then I get 500 down and 70 up.

However if I test with an IPv4 endpoint the download speed is only around 100mbps. Is this a result of the way MAP-T works (ie a bottleneck) or is it something else? I've tried both the Sky router and my own Openwrt one.

Re: MAP-T IPv4 speeds

-rpnz- — Mon, 20 Apr 2026 15:01:20 GMT

Hi @WhiskerP

MAP-T itself shouldn't be restricting speeds like that; although IPv4 does have to go via an additional router for the MAP-T translation in our design, one of the main benefits of MAP-T over other technologies, is that it's stateless and "easy" for routers to do that translation.

In general though, IPv4 and IPv6 are different routing tables, so even if you are using the exact same speed test server, the packets may traverse the internet via different paths. What speed test application and servers are you using?

Re: MAP-T IPv4 speeds

WhiskerP — Mon, 20 Apr 2026 16:03:39 GMT

Speedtest.net is OK but Speedof.me and openspeedtest.com are slow. I have a cloud server so I used iperf3 and again IPv4 was 100M whereas IPv6 was 500M.

Re: MAP-T IPv4 speeds

WhiskerP — Sat, 25 Apr 2026 08:37:46 GMT

Thanks. MAP-T requires more CPU than the router I tried. It's now running at full speed.

Regards

Peter

Re: MAP-T IPv4 speeds

-rpnz- — Mon, 27 Apr 2026 11:34:41 GMT

@WhiskerP wrote:
Thanks. MAP-T requires more CPU than the router I tried. It's now running at full speed.

In general MAP-T shouldn't do, but I'd take a guess that your combination of OpenWRT + Hardware means that MAP-T isn't getting hardware accelerated like forwarding native IPv4 or IPv6 is.

i.e. native IPv4 & IPv6 goes via the "fastpath" and forwarded in hardware, but the MAP-T translation has to be done in software/by the CPU or "slowpath".

Hardware accelleration requires support by both the hardware vendor and OpenWRT together. Might start working in future updates?

Re: MAP-T IPv4 speeds

WhiskerP — Tue, 28 Apr 2026 06:12:37 GMT

I had been running an Asus RT-AX53 OpenWRT 25.12.2 which struggled above 200Mbps even though top showed 70% free CPU. It's a dual core 880MHz Mediatek. I got hold of a cheap half price used Asus TUF AX-4200 which is quad core 2GHz ARM and it was definitely no problem!. But I was then asking about how to ensure port forwarding and I think someone at Sky has set my line to dual stack because MAP-T is no longer being offered. Thank you!

Re: MAP-T IPv4 speeds

Chrisee — Tue, 28 Apr 2026 06:23:15 GMT

@WhiskerP Sky can only use MAP-T sharing if the router advertises support for DHCPv6 Option95 which by default the Sky Max hub SR213 does but your Asus router will not be doing hence you are offered a dual stack connection.

Re: MAP-T IPv4 speeds

WhiskerP — Tue, 28 Apr 2026 06:26:56 GMT

It do have the Option 95 DUID value set and it was offering MAP-T to the Asus which was setting up a working IPv4 tunnel hence the original question.