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350 lines
13 KiB
Markdown
350 lines
13 KiB
Markdown
# Overview
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This document explains how to enable VoIP relaying on your homeserver with
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TURN.
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The synapse Matrix homeserver supports integration with TURN server via the
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[TURN server REST API](<https://tools.ietf.org/html/draft-uberti-behave-turn-rest-00>). This
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allows the homeserver to generate credentials that are valid for use on the
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TURN server through the use of a secret shared between the homeserver and the
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TURN server.
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The following sections describe how to install [coturn](<https://github.com/coturn/coturn>) (which implements the TURN REST API) and integrate it with synapse.
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## Requirements
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For TURN relaying with `coturn` to work, it must be hosted on a server/endpoint with a public IP.
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Hosting TURN behind NAT requires port forwaring and for the NAT gateway to have a public IP.
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However, even with appropriate configuration, NAT is known to cause issues and to often not work.
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## `coturn` setup
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### Initial installation
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The TURN daemon `coturn` is available from a variety of sources such as native package managers, or installation from source.
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#### Debian installation
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Just install the debian package:
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```sh
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apt install coturn
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```
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This will install and start a systemd service called `coturn`.
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#### Source installation
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1. Download the [latest release](https://github.com/coturn/coturn/releases/latest) from github. Unpack it and `cd` into the directory.
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1. Configure it:
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```sh
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./configure
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```
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You may need to install `libevent2`: if so, you should do so in
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the way recommended by your operating system. You can ignore
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warnings about lack of database support: a database is unnecessary
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for this purpose.
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1. Build and install it:
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```sh
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make
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make install
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```
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### Configuration
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1. Create or edit the config file in `/etc/turnserver.conf`. The relevant
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lines, with example values, are:
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```
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use-auth-secret
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static-auth-secret=[your secret key here]
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realm=turn.myserver.org
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```
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See `turnserver.conf` for explanations of the options. One way to generate
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the `static-auth-secret` is with `pwgen`:
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```sh
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pwgen -s 64 1
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```
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A `realm` must be specified, but its value is somewhat arbitrary. (It is
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sent to clients as part of the authentication flow.) It is conventional to
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set it to be your server name.
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1. You will most likely want to configure coturn to write logs somewhere. The
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easiest way is normally to send them to the syslog:
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```sh
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syslog
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```
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(in which case, the logs will be available via `journalctl -u coturn` on a
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systemd system). Alternatively, coturn can be configured to write to a
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logfile - check the example config file supplied with coturn.
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1. Consider your security settings. TURN lets users request a relay which will
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connect to arbitrary IP addresses and ports. The following configuration is
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suggested as a minimum starting point:
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```
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# VoIP traffic is all UDP. There is no reason to let users connect to arbitrary TCP endpoints via the relay.
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no-tcp-relay
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# don't let the relay ever try to connect to private IP address ranges within your network (if any)
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# given the turn server is likely behind your firewall, remember to include any privileged public IPs too.
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denied-peer-ip=10.0.0.0-10.255.255.255
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denied-peer-ip=192.168.0.0-192.168.255.255
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denied-peer-ip=172.16.0.0-172.31.255.255
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# recommended additional local peers to block, to mitigate external access to internal services.
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# https://www.rtcsec.com/article/slack-webrtc-turn-compromise-and-bug-bounty/#how-to-fix-an-open-turn-relay-to-address-this-vulnerability
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no-multicast-peers
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denied-peer-ip=0.0.0.0-0.255.255.255
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denied-peer-ip=100.64.0.0-100.127.255.255
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denied-peer-ip=127.0.0.0-127.255.255.255
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denied-peer-ip=169.254.0.0-169.254.255.255
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denied-peer-ip=192.0.0.0-192.0.0.255
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denied-peer-ip=192.0.2.0-192.0.2.255
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denied-peer-ip=192.88.99.0-192.88.99.255
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denied-peer-ip=198.18.0.0-198.19.255.255
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denied-peer-ip=198.51.100.0-198.51.100.255
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denied-peer-ip=203.0.113.0-203.0.113.255
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denied-peer-ip=240.0.0.0-255.255.255.255
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# special case the turn server itself so that client->TURN->TURN->client flows work
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# this should be one of the turn server's listening IPs
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allowed-peer-ip=10.0.0.1
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# consider whether you want to limit the quota of relayed streams per user (or total) to avoid risk of DoS.
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user-quota=12 # 4 streams per video call, so 12 streams = 3 simultaneous relayed calls per user.
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total-quota=1200
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```
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1. Also consider supporting TLS/DTLS. To do this, add the following settings
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to `turnserver.conf`:
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```
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# TLS certificates, including intermediate certs.
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# For Let's Encrypt certificates, use `fullchain.pem` here.
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cert=/path/to/fullchain.pem
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# TLS private key file
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pkey=/path/to/privkey.pem
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# Ensure the configuration lines that disable TLS/DTLS are commented-out or removed
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#no-tls
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#no-dtls
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```
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In this case, replace the `turn:` schemes in the `turn_uris` settings below
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with `turns:`.
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We recommend that you only try to set up TLS/DTLS once you have set up a
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basic installation and got it working.
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NB: If your TLS certificate was provided by Let's Encrypt, TLS/DTLS will
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not work with any Matrix client that uses Chromium's WebRTC library. This
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currently includes Element Android & iOS; for more details, see their
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[respective](https://github.com/vector-im/element-android/issues/1533)
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[issues](https://github.com/vector-im/element-ios/issues/2712) as well as the underlying
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[WebRTC issue](https://bugs.chromium.org/p/webrtc/issues/detail?id=11710).
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Consider using a ZeroSSL certificate for your TURN server as a working alternative.
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1. Ensure your firewall allows traffic into the TURN server on the ports
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you've configured it to listen on (By default: 3478 and 5349 for TURN
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traffic (remember to allow both TCP and UDP traffic), and ports 49152-65535
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for the UDP relay.)
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1. If your TURN server is behind NAT, the NAT gateway must have an external,
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publicly-reachable IP address. You must configure coturn to advertise that
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address to connecting clients:
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```
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external-ip=EXTERNAL_NAT_IPv4_ADDRESS
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```
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You may optionally limit the TURN server to listen only on the local
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address that is mapped by NAT to the external address:
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```
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listening-ip=INTERNAL_TURNSERVER_IPv4_ADDRESS
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```
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If your NAT gateway is reachable over both IPv4 and IPv6, you may
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configure coturn to advertise each available address:
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```
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external-ip=EXTERNAL_NAT_IPv4_ADDRESS
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external-ip=EXTERNAL_NAT_IPv6_ADDRESS
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```
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When advertising an external IPv6 address, ensure that the firewall and
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network settings of the system running your TURN server are configured to
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accept IPv6 traffic, and that the TURN server is listening on the local
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IPv6 address that is mapped by NAT to the external IPv6 address.
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1. (Re)start the turn server:
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* If you used the Debian package (or have set up a systemd unit yourself):
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```sh
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systemctl restart coturn
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```
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* If you installed from source:
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```sh
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bin/turnserver -o
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```
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## Synapse setup
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Your homeserver configuration file needs the following extra keys:
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1. "`turn_uris`": This needs to be a yaml list of public-facing URIs
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for your TURN server to be given out to your clients. Add separate
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entries for each transport your TURN server supports.
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2. "`turn_shared_secret`": This is the secret shared between your
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homeserver and your TURN server, so you should set it to the same
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string you used in turnserver.conf.
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3. "`turn_user_lifetime`": This is the amount of time credentials
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generated by your homeserver are valid for (in milliseconds).
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Shorter times offer less potential for abuse at the expense of
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increased traffic between web clients and your homeserver to
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refresh credentials. The TURN REST API specification recommends
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one day (86400000).
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4. "`turn_allow_guests`": Whether to allow guest users to use the
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TURN server. This is enabled by default, as otherwise VoIP will
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not work reliably for guests. However, it does introduce a
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security risk as it lets guests connect to arbitrary endpoints
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without having gone through a CAPTCHA or similar to register a
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real account.
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As an example, here is the relevant section of the config file for `matrix.org`. The
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`turn_uris` are appropriate for TURN servers listening on the default ports, with no TLS.
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turn_uris: [ "turn:turn.matrix.org?transport=udp", "turn:turn.matrix.org?transport=tcp" ]
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turn_shared_secret: "n0t4ctuAllymatr1Xd0TorgSshar3d5ecret4obvIousreAsons"
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turn_user_lifetime: 86400000
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turn_allow_guests: True
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After updating the homeserver configuration, you must restart synapse:
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* If you use synctl:
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```sh
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# Depending on how Synapse is installed, synctl may already be on
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# your PATH. If not, you may need to activate a virtual environment.
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synctl restart
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```
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* If you use systemd:
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```sh
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systemctl restart matrix-synapse.service
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```
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... and then reload any clients (or wait an hour for them to refresh their
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settings).
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## Troubleshooting
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The normal symptoms of a misconfigured TURN server are that calls between
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devices on different networks ring, but get stuck at "call
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connecting". Unfortunately, troubleshooting this can be tricky.
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Here are a few things to try:
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* Check that you have opened your firewall to allow TCP and UDP traffic to the
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TURN ports (normally 3478 and 5349).
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* Check that you have opened your firewall to allow UDP traffic to the UDP
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relay ports (49152-65535 by default).
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* Try disabling `coturn`'s TLS/DTLS listeners and enable only its (unencrypted)
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TCP/UDP listeners. (This will only leave signaling traffic unencrypted;
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voice & video WebRTC traffic is always encrypted.)
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* Some WebRTC implementations (notably, that of Google Chrome) appear to get
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confused by TURN servers which are reachable over IPv6 (this appears to be
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an unexpected side-effect of its handling of multiple IP addresses as
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defined by
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[`draft-ietf-rtcweb-ip-handling`](https://tools.ietf.org/html/draft-ietf-rtcweb-ip-handling-12)).
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Try removing any AAAA records for your TURN server, so that it is only
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reachable over IPv4.
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* If your TURN server is behind NAT:
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* double-check that your NAT gateway is correctly forwarding all TURN
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ports (normally 3478 & 5349 for TCP & UDP TURN traffic, and 49152-65535 for the UDP
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relay) to the NAT-internal address of your TURN server. If advertising
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both IPv4 and IPv6 external addresses via the `external-ip` option, ensure
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that the NAT is forwarding both IPv4 and IPv6 traffic to the IPv4 and IPv6
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internal addresses of your TURN server. When in doubt, remove AAAA records
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for your TURN server and specify only an IPv4 address as your `external-ip`.
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* ensure that your TURN server uses the NAT gateway as its default route.
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* Enable more verbose logging in coturn via the `verbose` setting:
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```
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verbose
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```
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... and then see if there are any clues in its logs.
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* If you are using a browser-based client under Chrome, check
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`chrome://webrtc-internals/` for insights into the internals of the
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negotiation. On Firefox, check the "Connection Log" on `about:webrtc`.
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(Understanding the output is beyond the scope of this document!)
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* You can test your Matrix homeserver TURN setup with <https://test.voip.librepush.net/>.
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Note that this test is not fully reliable yet, so don't be discouraged if
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the test fails.
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[Here](https://github.com/matrix-org/voip-tester) is the github repo of the
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source of the tester, where you can file bug reports.
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* There is a WebRTC test tool at
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<https://webrtc.github.io/samples/src/content/peerconnection/trickle-ice/>. To
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use it, you will need a username/password for your TURN server. You can
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either:
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* look for the `GET /_matrix/client/r0/voip/turnServer` request made by a
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matrix client to your homeserver in your browser's network inspector. In
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the response you should see `username` and `password`. Or:
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* Use the following shell commands:
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```sh
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secret=staticAuthSecretHere
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u=$((`date +%s` + 3600)):test
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p=$(echo -n $u | openssl dgst -hmac $secret -sha1 -binary | base64)
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echo -e "username: $u\npassword: $p"
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```
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Or:
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* Temporarily configure coturn to accept a static username/password. To do
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this, comment out `use-auth-secret` and `static-auth-secret` and add the
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following:
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```
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lt-cred-mech
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user=username:password
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```
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**Note**: these settings will not take effect unless `use-auth-secret`
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and `static-auth-secret` are disabled.
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Restart coturn after changing the configuration file.
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Remember to restore the original settings to go back to testing with
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Matrix clients!
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If the TURN server is working correctly, you should see at least one `relay`
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entry in the results.
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