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+# coturn TURN server
+
+The following sections describe how to install [coturn](<https://github.com/coturn/coturn>) (which implements the TURN REST API).
+
+## `coturn` setup
+
+### Initial installation
+
+The TURN daemon `coturn` is available from a variety of sources such as native package managers, or installation from source.
+
+#### Debian and Ubuntu based distributions
+
+Just install the debian package:
+
+```sh
+sudo apt install coturn
+```
+
+This will install and start a systemd service called `coturn`.
+
+#### Source installation
+
+1. Download the [latest release](https://github.com/coturn/coturn/releases/latest) from github. Unpack it and `cd` into the directory.
+
+1. Configure it:
+
+ ```sh
+ ./configure
+ ```
+
+ You may need to install `libevent2`: if so, you should do so in
+ the way recommended by your operating system. You can ignore
+ warnings about lack of database support: a database is unnecessary
+ for this purpose.
+
+1. Build and install it:
+
+ ```sh
+ make
+ sudo make install
+ ```
+
+### Configuration
+
+1. Create or edit the config file in `/etc/turnserver.conf`. The relevant
+ lines, with example values, are:
+
+ ```
+ use-auth-secret
+ static-auth-secret=[your secret key here]
+ realm=turn.myserver.org
+ ```
+
+ See `turnserver.conf` for explanations of the options. One way to generate
+ the `static-auth-secret` is with `pwgen`:
+
+ ```sh
+ pwgen -s 64 1
+ ```
+
+ A `realm` must be specified, but its value is somewhat arbitrary. (It is
+ sent to clients as part of the authentication flow.) It is conventional to
+ set it to be your server name.
+
+1. You will most likely want to configure `coturn` to write logs somewhere. The
+ easiest way is normally to send them to the syslog:
+
+ ```sh
+ syslog
+ ```
+
+ (in which case, the logs will be available via `journalctl -u coturn` on a
+ systemd system). Alternatively, `coturn` can be configured to write to a
+ logfile - check the example config file supplied with `coturn`.
+
+1. Consider your security settings. TURN lets users request a relay which will
+ connect to arbitrary IP addresses and ports. The following configuration is
+ suggested as a minimum starting point:
+
+ ```
+ # VoIP traffic is all UDP. There is no reason to let users connect to arbitrary TCP endpoints via the relay.
+ no-tcp-relay
+
+ # don't let the relay ever try to connect to private IP address ranges within your network (if any)
+ # given the turn server is likely behind your firewall, remember to include any privileged public IPs too.
+ denied-peer-ip=10.0.0.0-10.255.255.255
+ denied-peer-ip=192.168.0.0-192.168.255.255
+ denied-peer-ip=172.16.0.0-172.31.255.255
+
+ # recommended additional local peers to block, to mitigate external access to internal services.
+ # https://www.rtcsec.com/article/slack-webrtc-turn-compromise-and-bug-bounty/#how-to-fix-an-open-turn-relay-to-address-this-vulnerability
+ no-multicast-peers
+ denied-peer-ip=0.0.0.0-0.255.255.255
+ denied-peer-ip=100.64.0.0-100.127.255.255
+ denied-peer-ip=127.0.0.0-127.255.255.255
+ denied-peer-ip=169.254.0.0-169.254.255.255
+ denied-peer-ip=192.0.0.0-192.0.0.255
+ denied-peer-ip=192.0.2.0-192.0.2.255
+ denied-peer-ip=192.88.99.0-192.88.99.255
+ denied-peer-ip=198.18.0.0-198.19.255.255
+ denied-peer-ip=198.51.100.0-198.51.100.255
+ denied-peer-ip=203.0.113.0-203.0.113.255
+ denied-peer-ip=240.0.0.0-255.255.255.255
+
+ # special case the turn server itself so that client->TURN->TURN->client flows work
+ # this should be one of the turn server's listening IPs
+ allowed-peer-ip=10.0.0.1
+
+ # consider whether you want to limit the quota of relayed streams per user (or total) to avoid risk of DoS.
+ user-quota=12 # 4 streams per video call, so 12 streams = 3 simultaneous relayed calls per user.
+ total-quota=1200
+ ```
+
+1. Also consider supporting TLS/DTLS. To do this, add the following settings
+ to `turnserver.conf`:
+
+ ```
+ # TLS certificates, including intermediate certs.
+ # For Let's Encrypt certificates, use `fullchain.pem` here.
+ cert=/path/to/fullchain.pem
+
+ # TLS private key file
+ pkey=/path/to/privkey.pem
+
+ # Ensure the configuration lines that disable TLS/DTLS are commented-out or removed
+ #no-tls
+ #no-dtls
+ ```
+
+ In this case, replace the `turn:` schemes in the `turn_uris` settings below
+ with `turns:`.
+
+ We recommend that you only try to set up TLS/DTLS once you have set up a
+ basic installation and got it working.
+
+ NB: If your TLS certificate was provided by Let's Encrypt, TLS/DTLS will
+ not work with any Matrix client that uses Chromium's WebRTC library. This
+ currently includes Element Android & iOS; for more details, see their
+ [respective](https://github.com/vector-im/element-android/issues/1533)
+ [issues](https://github.com/vector-im/element-ios/issues/2712) as well as the underlying
+ [WebRTC issue](https://bugs.chromium.org/p/webrtc/issues/detail?id=11710).
+ Consider using a ZeroSSL certificate for your TURN server as a working alternative.
+
+1. Ensure your firewall allows traffic into the TURN server on the ports
+ you've configured it to listen on (By default: 3478 and 5349 for TURN
+ traffic (remember to allow both TCP and UDP traffic), and ports 49152-65535
+ for the UDP relay.)
+
+1. If your TURN server is behind NAT, the NAT gateway must have an external,
+ publicly-reachable IP address. You must configure `coturn` to advertise that
+ address to connecting clients:
+
+ ```
+ external-ip=EXTERNAL_NAT_IPv4_ADDRESS
+ ```
+
+ You may optionally limit the TURN server to listen only on the local
+ address that is mapped by NAT to the external address:
+
+ ```
+ listening-ip=INTERNAL_TURNSERVER_IPv4_ADDRESS
+ ```
+
+ If your NAT gateway is reachable over both IPv4 and IPv6, you may
+ configure `coturn` to advertise each available address:
+
+ ```
+ external-ip=EXTERNAL_NAT_IPv4_ADDRESS
+ external-ip=EXTERNAL_NAT_IPv6_ADDRESS
+ ```
+
+ When advertising an external IPv6 address, ensure that the firewall and
+ network settings of the system running your TURN server are configured to
+ accept IPv6 traffic, and that the TURN server is listening on the local
+ IPv6 address that is mapped by NAT to the external IPv6 address.
+
+1. (Re)start the turn server:
+
+ * If you used the Debian package (or have set up a systemd unit yourself):
+ ```sh
+ sudo systemctl restart coturn
+ ```
+
+ * If you built from source:
+
+ ```sh
+ /usr/local/bin/turnserver -o
+ ```
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