AirPort Extreme AC (6th gen) actually supports 1 Gigabit wired throughput speed on IPv4, but not IPv6!
So I finally upgraded to a gigabit internet connection. I had previously rewired my house with quality Cat 6 cables to I was curious to know how good a job I did. My internet setup is a direct fiber optic line from the node to the ISP gateway/modem (in passthrough mode) to the AirPort Extreme serving as the router/DHCP server and WiFi access point. All copper connections are via at least Gigabit Ethernet ports and Cat 6 terminations.
In all the forums I've come across, everyone references the SmallNetBuider review claiming a max throughput between 300 - 400 Mbps in router mode or 500 - 600 Mbps in bridge mode.
Attached are my Speedtest results using 4 different servers: 2 IPv4 and 2 IPv6. The bottom 4 results (10:xx am) are a direct wired passthrough connection from the modem to my Mac. The top 4 results (11:00 am) are a wired passthrough connection via the AirPort Extreme to my Mac.
My ISP advertises a speed of 940 Mbps. As expected the bottom 4 results are all consistently around the max speed. The top 4 however diverge based on whether the testing server established an IPv4 or IPv6 connection. The 2 IPv4 connections result in download speeds of 918 and 947 Mbps. The 2 IPv6 connections result in download speeds of 647 and 644 Mbps.
So clearly the AEAC actually supports gigabit speeds. My fastest ever recorded speed is actually 947 Mbps, via the AirPort Extreme! Firstly, to me this brings into question the veracity of SmallNetBuilder testing and reviews. Second, and more importantly for me, what is the Airport doing with IPv6 connections that is causing the speed to reduce to only 2/3rds of the IPv4 connection speed? Can I change any settings to actually get full speeds via IPv6?
My IPv6 setup in Airport Utility is Automatic in Native mode and IPv6 Connection Sharing enabled. IGMP Snooping is enabled and incoming IPv6 connections are blocked.
This was quite a surprise to me that a 10 year old router can support this kind of throughput. I'm really curious why others are not able to achieve this as well. But I'm happy to add this datapoint!