Why your AC wifi can't reach full speed on 3.13 kernel (Ubuntu 14.04, Mint 17, elementaryOS)

Less-known depths of wireless: regulations by countries and non-existent updates for linux.

I’ve recently bought a new Wifi router, a Linksys WRT1900AC1. Not only for the speed, but also because it was marketed as a hacker-friendly router, with no locks and tricks to replace the firmware with OpenWRT2. ( We had to wait for OpenWRT to support the AC speed, but it’s all fine now. ).

What I was not counting on is the rusty knowledge of mine on wireless. I’ve set up everything, test, wow, much speed, such 900Mbit/s. Until started fine tuning and added the Regulatory Country Code - and got stuck with 300Mbit/s.

I already knew about the per country limitations ( bureaucracy… Vogons… ) - what I was unaware of is the fact that this sometimes gets updated3 and that the linux you have never updates it on it’s own.

kernel 3.13.0-57-generic ( which is the thing in Ubuntu 14.04 LTS, Trusty Tahr and also in elementaryOS Freya )

Ubuntu 14.04 Current online version
Country 00 (2402 - 2472 @ 40) (2402 - 2472 @ 40)
(2457 - 2482 @ 40) (2457 - 2482 @ 40)
(2474 - 2494 @ 20) (2474 - 2494 @ 20)
(5170 - 5250 @ 40) (5170 - 5250 @ 80)
(5735 - 5835 @ 40) (5250 - 5330 @ 80)
(5490 - 5730 @ 160)
(5735 - 5835 @ 80)
(57240 - 63720 @ 2160)
country GB: (2402 - 2482 @ 40) (2402 - 2482 @ 40)
(5170 - 5250 @ 40) (5170 - 5250 @ 80)
(5250 - 5330 @ 40) (5250 - 5330 @ 80)
(5490 - 5710 @ 40) (5490 - 5710 @ 160)
(57240 - 65880 @ 2160) (57000 - 66000 @ 2160)

See the difference? no ‘@ 80’ or ‘@ 160’ for GB in the 3.13 kernel. That is why I was stuck on 300Mbit/s ( 40Mhz width ).

So after a ridiculosly long search I’ve found Rick Deckardt’s entry on the topic4 which finally helped me solve the issue.

Short story:

#!/bin/bash

cd ~
# this is the current version by the time I'm writing this post;
# go and check the updates before blindly copy-pasting
cur="2015.04.06"
wget "http://kernel.org/pub/software/network/wireless-regdb/wireless-regdb-${cur}.tar.xz"
tar xJf "wireless-regdb-${cur}.tar.xz"
cd "wireless-regdb-${cur}"
make
sudo cp regulatory.bin /lib/crda/regulatory.bin
sudo cp *.pem /lib/crda/pubkeys
sudo reboot

Read more:


  1. http://www.linksys.com/us/p/P-WRT1900AC/

  2. http://wiki.openwrt.org/toh/linksys/wrt1900ac

  3. http://drvbp1.linux-foundation.org/~mcgrof/rel-html/wireless-regdb/

  4. http://deckardt.nl/blog/2011/01/20/regulatory-limitations-in-linux-wireless/



Encourage creation!

If this entry helped you, or you simply liked it, leave a tip.