Following up with our WiFi chipset vendor and testing to clear up any confusion.
Late to the party jemanner, but I suspect your problem is the latest firmware for the RT-AC68U breaks 2.4Ghz for many devices. You can either roll back to a previous firmware version until this gets fixed or there is a work around where you can go into 2.4Ghz wireless settings on the router and enable ālegacy mode.ā This limits the 2.4Ghz band to b and g wifi (turns off n), but gets around the bug and will allow you to get your Rachio device up and running.
Had the same issue here on my RT-AC68P.
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Iām at the latest firmware on the RT-AC68U, 3.0.0.4.380_1842. In Auto mode, with b/g Protection checked. If anything, the problem was with firmware a step or two back. All devices are working great.
Iāve spoken with our WiFi vendor and support team. The consensus is it should work, but weāve seen some routers where it doesnāt.
WiFi vendor:
Yes, the router knows which client is connected at which band and would take care of the bridging between the 2.4G band and 5G band.
Rachio support:
Iāve had users confirm dual band works, others say it doesnāt ā might depend on how the router handles dual band
Hope that adds a little more light on the subject 
@david, great question. @jemanner nailed the answer. WiFi range was is critical for the controller as many users have it installed in garages, basements, sheds, etc. Unfortunately, 5ghz has a limited range (the higher the frequency, the shorter the range).
I believe the key variable with dual band routers is how they manage the dual bands. There are two types of dual band routers in the market; Simultaneous and Selectable. Each has very different capabilities and performance:
As you can see, Simultaneous dual band routers provide the ultimate in flexibility and performance by providing two independent, dedicated networks.
This 3rd party article does a nice job explaining how both types of dual band routers can react using a common printer example.
Hope this helps.
Best, Emil
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Really late to the party here but there is a 3rd party firmware for the rt86u and other asus routers called Merlin. It is basically the out of box firmware made more secure and reliable. Havenāt had any issues with it. Highly recommend. This is one of the best routers I have ever used to date.
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Can one revert back to the Asus firmware if they donāt like Merlin? However, Iām doing great with my Rachio Gen 2 at the moment. Both bands on the RT-AC68U are active, and the Rachio is happy.
If Iām not mistaken, Merlin (donāt know his real name) is actually used by ASUS to help them with firmware sometimes; Merlin just makes his own that has added stuff. Iāve heard very good things about it. There are also dd-wrt and xVortex.
I use two dual-band routers and have everything turned on with no issues with my current Rachio v1. Having the 5Ghz turned on should have NO effect on the Rachio as it canāt even āseeā that frequency.
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Gen 1 & Gen 2 Works fine with my dual band router (apple). It just connects on 2.4ghz and knows nothing about the 5ghz.
Iāll also add another plug for ubiquity as mentioned by @plainsane. I have also recently started using open-mesh and been pretty happy as well. Both have very responsive support, but as mentioned a bit more for tinkerer.
I just canāt get a single router to cover my house/garage.
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Yes you can go back and forth from Merlin to stock. But you wonāt ever want/need to. he provides a lot of patches to asus bugs in his builds that they pick up.
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Not a perfect solution but after struggling with this issue and finding a brief note about the 5ghz band in the manual I adding an additional dedicated AP for the rachio and it worked perfect. Iāve decided to add all my home automation devices to this second SSID to separate it from my other devices.
For anyone that is curious I had 2 Aruba IAP-205s. Iām actually using the AP on my FIOS router as the second network. I could have probably easily created a second SSID on the APs but this other option was easier/quicker.
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