RT-AC66U - During heavy download CPU maxes & WiFi fails - is this normal?

[Ian B]

I bought this RT-AC66U from eBay in Dec 2015 and it's been my main router and WiFi in my house. I used in for a few weeks on the standard Asus FW before installing Merlin on it.

I've been generally very pleased with the router. I have set up parental controls to stop internet for certain devices from 9pm to 6am. Other than that I have not made many changes to the settings.

I loaded MySQL onto an external USB stick by following this guide:
http://hints.dk/en/2013/03/13/mysql-server-on-rt-n66u-or-rt-ac66u-for-shared-xbmc-library/

I had intended to point my Kodi boxes at the MySQL instance in order to share their libraries but I have not got around to it yet.

I have a Virgin Media 100Mbps cable connection (in the UK) and it is pretty quick.

Over the last few months I noticed that whenever I was downloading a large amount of data on my PC (cabled to the router) the WiFi would drop for other users. This was anything from opening Steam and waiting for it to install updates, opening Dropbox and waiting for it to Sync large files, but most easily replicated by downloading a Torrent file such as a Linux ISO.

I logged in to the router web interface and noticed that the CPU would spike to almost 100% for the duration of the download. The web interface would then become almost unresponsive then update only every 30 seconds or so. As soon as I stopped the download the CPU would drop to normal and the web interface would be back to normal.

I removed the USB stick with MySQL installed on it and power cycled the router but it made no difference. So I assume that MySQL is nothing to do with the problem (but then I am not sure!)

I had a look around online and I found a lot of people saying that this is typical of a 'home grade' router and they are just not capable of handling lots of connections on a fast connection.

So I have swapped the Asus out at the moment and I am using Sophos UTM on a Dell dual-core PC with 3GB RAM. This has not got any problem with the issues above. I can download 'to the max' and still everyone is happy on WiFi (the Asus is now just working as a WAP) streaming Netflix etc.

But someone recently suggested to me that the Asus should work just fine and maybe the firmware was the problem. He was using an even older piece of hardware (Netgear WNTR2200 running Open-WRT) and it was perfectly capable of providing WiFi while doing heavy download.

I have updated Merlin a couple of times during the issues I was having, the last time I updated was perhaps 4 weeks ago (sorry I can't remember the current FW version, I can check when I get home).

I guess I should remove the USB stick and factory reset the router to wipe MySQL and all settings to test. But before I do this here is the question:

Is this Asus RT-AC66U running Merlin powerful enough for my needs?

Thanks, Ian

 

[Ian B]

Maybe I wrote too much ...

TL;DR =

Surely somebody can comment on whether their Merlin/Asus AC66U can handle a heavy download at the same time as WiFi on a fast connection?

Edit: I checked and I am on 380.65 FW

 

[mstombs]

I don't think wifi dropping out is normal, but if cpu maxing out anything can happen, there is a reason all the newer routers have faster dual core ARM processors. The N66U can speedtest over 220Mbps on UK VM 200/12 Mbps service (despite the Intel Puma 6 bugged Hub 3.0 cable modem) - but only with hardware acceleration (Broadcom CTF) turned on, which means no IP accounting, QOS etc. Have you tried this?

 

[Ian B]

Thanks mstombs, I have not tested with changes to hardware acceleration. I searched these forums a little more deeply and it seems I am not alone with this issue, it seems that USB disk or various other services can cause the CPU to max out. I also discovered posts that said that if hardware acceleration is turned off then parental controls is not going to work. That would be a showstopper for me.

I think I will wipe the Asus and start over without a USB pendrive attached. I can then see what effect turning on/off hardware acceleration has and whether I can get the performance I need.

 

[cybrnook]

I assume since you are using things like parental controls, then HW acceleration is being disabled in the process. The N66U has a little Mips processor (Not as strong as the bigger brother ARM Asus routers like the RT-AC68U that is one step up, as long as it's not the B1 which obviously it's not). I think what is likely happening is you are maxing your processing speed out as HW accell is disabled (likely).

I don't see a good way around this if you are dead set on using parental controls. The ARM based routers can handle around 300 or so mbps without HW accell, I think that is likely what you would want to look at. Or just use your 66U as an access point. Sounds like you would benefit from a dash of QoS as well, which also requires the disabling of HW accell...

 

[Ian B]

I've done some work so I'll share my results.

I removed the USB pendrive, wiped the Asus and updated to Firmware:380.65_4 while I was at it. I swapped it into my network instead of the Sophos UTM and started testing.

I found that in it's default set up I can download 'to the max' and the CPU of the Asus stays below 50% and everything runs fine. Kids can be watching Netflix on iPad and so on.

If I go to the Tools page I see: HW acceleration Enabled

If I turn on Parental Controls then everything stays OK as well. HW acc. stays Enabled. Unfortunately the Parental Controls page recommends turning off NAT Acceleration "for more precise scheduling control". I found out more about this here: https://www.snbforums.com/threads/parental-control-time-scheduling-not-working.27322/ so it seems I really need to turn off NAT Acceleration otherwise Parental Controls is basically ineffective.

When I disable NAT Acceleration (and I continue with my heavy downloading) then the CPU becomes very busy (60%+), WiFi drops and the Asus admin page becomes very slow and unresponsive. The Tools page says: HW acceleration Disabled (by user)

So that is it. Fast connection and heavy downloading is incompatible with running Parental Controls on this level of router. At least I got to the bottom of the problem. Time to turn my Router into a WAP and put back the Sophos UTM (on my spare PC) as a router.

 

[kingarthas]

I see quite a lot of people have similar problem... I got issues too ASUS RT-N66U merlin 380.68_4... I have 2 VPN server one TUN and one TAP. I stop shared HDD and media server and it got better, however still got high CPU load when downloading via WIFI. At about 6MByte/s (50mbit) I got 70% CPU load and speed drop from time to time. If connected on LAN at same download speed CPU load is 10%, and again have some drops in the speed every 1min or so. It was not like that in the past...

Few years back i got similar issues with Asus firmware, however since i run merlin all was good .

 

[ckong]

I know this is an aging thread but wanted to post since I recently received an upgrade from 60/4 mbps to 100/10 mbps download/upload speeds respectively. I also upgraded from an RT-AC66U to a RT-AC3100. QoS enabled on both during speed tests (so hardware acceleration disabled). The RT-AC66U was able to keep with the 60/4 speeds, but when Spectrum (formally Charter Cable) upgraded my speeds, I was only able to get roughly 88/10. The RT-AC66U wasn't able to keep up with the max download speed. Fast forward a little bit and now I have the RT-AC3100 installed. Speed tests show 115/12. I know these are burst speeds and Spectrum's system auto-throttles down to 100/10 after a couple of minutes, but it was nice to see the new router handles faster throughput with no problems (tested with both wired and wireless connections).

Btw, I only upgraded from the RT-AC66U because I thought a power spike fried the router. After re-flashing it (several times), it eventually was brought back to life. It continued to be my main router for several more weeks afterwards till I got the RT-AC3100. The RT-AC66U is now my hot-standby.