===== Central Regulatory Domain Agent =====

CRDA acts as the udev helper for communication between the kernel and userspace for regulatory compliance. It relies on [[en/developers/Documentation/nl80211|nl80211]] for communication. CRDA is intended to be run only through udev communication from the kernel. The user should never have to run it manually except if debugging udev issues. 


===== License =====

CRDA is licensed under the [[https://raw.github.com/richardfontana/copyleft-next/master/Releases/copyleft-next-0.3.0|copyleft-next]] license while [[en/developers/Regulatory/wireless-regdb|wireless-regdb]] is licensed under the [[wp>ISC_license|ISC license]]. 


===== Code =====

[[https://git.kernel.org/cgit/linux/kernel/git/mcgrof/crda.git/|https://git.kernel.org/cgit/linux/kernel/git/mcgrof/crda.git/]] 


<code>git://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/crda.git</code>

===== Releases =====

You can find official crda releases on the [[http://drvbp1.linux-foundation.org/~mcgrof/rel-html/crda/|crda release page]], older releases can be downloaded through the [[https://www.kernel.org/pub/software/network/crda/|crda archive]] 

===== Status =====

The new regulatory infrastructure went in as of 2.6.28, so CRDA can be used in kernels >= 2.6.28. It is required for 802.11d operation in 2.6.29.

CRDA is no longer needed as of kernel v4.15 since commit [[https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=007f6c5e6eb45 | 007f6c5e6eb45]] ("cfg80211: support loading regulatory database as firmware file") added support to use the kernel's firmware request API which looks for the firmware on /lib/firmware.

===== Host requirements =====
  * libc/ublibc 
  * regulatory.bin file 
  * libnl >= libnl1 
  * udevd [but read below for alternative] You can skip out on the CRDA and udev requirement by using CONFIG_CFG80211_INTERNAL_REGDB but read below on its own requirements. 


===== CONFIG_CFG80211_INTERNAL_REGDB =====

If you do not want to install CRDA on a host, you can simply enable the CONFIG_CFG80211_INTERNAL_REGDB on your kernel. Once enabled you can place the db.txt from the wireless-regdb into net/wireless/db.txt. The downside to using this option is that you will need to rebuild your kernel for any regulatory updates, therefore using CONFIG_CFG80211_INTERNAL_REGDB is not recommended. 

If using CONFIG_CFG80211_INTERNAL_REGDB without updating net/wireless/db.txt you'll end up with the static world regulatory domain, so if using CONFIG_CFG80211_INTERNAL_REGDB you should be sure to update net/wireless/db.txt otherwise you may end up spending a lot of time debugging an issue that does not exist. To help with this a patch has been sent to print a warning when a kernel has been built with CONFIG_CFG80211_INTERNAL_REGDB but the database is emtpy. If you happen to also have CONFIG_CFG80211_REG_DEBUG then compiling of the kernel will simply fail. 


===== Build requirements =====
    * python and the m2crypto package (python-m2crypto) 
    * libgcrypt or libssl (openssl) header files 
    * nl library and header files (libnl1 and libnl-dev) available at git://git.kernel.org/pub/scm/libs/netlink/libnl.git 
    * RSA public key of Seth Forshee, we include this as part of this package so you do not need to install it. This RSA public key comes from the wireless-regdb.git tree and we keep it up to date here. 
    * regulatory database (regulatory.bin, no need to build just put the file in REG_BIN location) from: 
<code>   git://git.kernel.org/pub/scm/linux/kernel/git/sforshee/wireless-regdb.git</code>

===== Letting the kernel call CRDA =====

We use userspace events (uevents) to let the kernel speak to userspace. Below is an example udev rule you can place into your distribution's udev rules directory (usually /etc/udev/rules.d/). Note that most distributions have udev configured with inotify on the udev rules directory, so there is no need to restart udev after adding the new rule. 


<code># Example file, should be put in /etc/udev/rules.d/regulatory.rules
KERNEL=="regulatory*", ACTION=="change", SUBSYSTEM=="platform", RUN+="/sbin/crda"</code>

===== Dynamic reading of trusted public keys =====

CRDA can be built with gcrypt or openssl support. If using openssl (USE_OPENSSL=1) you can enable dynamic loading of trusted public keys and stuff. Trusted public keys can be put into the directory: 


<code>/etc/wireless-regdb/pubkeys</code>
gcrypt support does not support reading public keys dynamically as gcrypt currently lacks a PEM parser. 


===== Changing regulatory domains =====


==== Helping compliance by allowing to change regulatory domains ====

Linux allows changing regulatory domains in compliance with regulatory restrictions world wide, including the US FCC. In order to achieve this devices always respect their programmed regulatory domain and a country code selection will only enhance regulatory restrictions. This is in accordance with the [[https://fjallfoss.fcc.gov/oetcf/kdb/forms/FTSSearchResultPage.cfm?switch=P&id=39498|FCC part 15 country code selection knowledge base publication number 594280]]. As an example if your device was programmed for operation in the US which allows operation on channels 1-11 on the 2.4 GHz band and you visit Japan which allows operation on channels 1-14 and you change your regulatory domain to JP you will not be able to use channel 12, 13 or 14 (CCK). But if you have a device programmed for operation in Japan and visit the US and you select US as your regulatory domain you will have channel 12-14 disabled. 

Userspace applications can request the kernel to change regulatory domains. The following userspace applications currently allow you to do this: 
      * [[en/users/Documentation/iw|iw]] 
      * the latest [[http://hostap.epitest.fi/wpa_supplicant/|wpa_supplicant]] (from the git tree) 


==== Using iw to change regulatory domains ====

You can use iw from the command line as follows: 


<code>iw reg set US</code>

==== Using wpa_supplicant to change regulatory domains ====

Get the [[http://hostap.epitest.fi/wpa_supplicant/|wpa_supplicant]] (as of 0.6.7) and then add as part of your configuration file a line that has something like this: 


<code>COUNTRY=US</code>

==== Using Network Manager to change regulatory domains ====

This needs to be implemented, but since Network Manager uses wpa_supplicant it should just be a matter of adding a user interface option to let a user select an alpha2 and then adding the country entry into the wpa_supplicant configuration entered. 


===== Debugging kernel to CRDA communication =====

To debug communication between the kernel and udev you can monitor udev events: 


<code>udevadm monitor --environment kernel</code>