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eturnal TURN server

The following sections describe how to install eturnal (which implements the TURN REST API).

`eturnal` setup

Initial installation

The eturnal TURN server implementation is available from a variety of sources such as native package managers, binary packages, installation from source or container image. They are all described here.

Quick-Test instructions in a Linux Shell or with Docker are available as well.

Configuration

After installation, eturnal usually ships a default configuration file here: /etc/eturnal.yml (and, if not found there, there is a backup file here: /opt/eturnal/etc/eturnal.yml). It uses the (indentation-sensitive!) YAML format. The file contains further explanations.

Here are some hints how to configure eturnal on your host machine or when using e.g. Docker. You may also further deep dive into the reference documentation.

eturnal runs out of the box with the default configuration. To enable TURN and to integrate it with your homeserver, some aspects in eturnal's default configuration file must be edited:

Homeserver's turn_shared_secret and eturnal's shared secret for authentication

Both need to have the same value. Uncomment and adjust this line in eturnal's configuration file:
```
secret: "long-and-cryptic"     # Shared secret, CHANGE THIS.
```
One way to generate a secret is with pwgen:
```
pwgen -s 64 1
```
Public IP address

If your TURN server is behind NAT, the NAT gateway must have an external, publicly-reachable IP address. eturnal tries to autodetect the public IP address, however, it may also be configured by uncommenting and adjusting this line, so eturnal advertises that address to connecting clients:
```
relay_ipv4_addr: "203.0.113.4" # The server's public IPv4 address.
```
If your NAT gateway is reachable over both IPv4 and IPv6, you may configure eturnal to advertise each available address:
```
relay_ipv4_addr: "203.0.113.4" # The server's public IPv4 address.
relay_ipv6_addr: "2001:db8::4" # The server's public IPv6 address (optional).
```
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.
Logging

If eturnal was started by systemd, log files are written into the /var/log/eturnal directory by default. In order to log to the journal instead, the log_dir option can be set to stdout in the configuration file.

Security considerations

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, see also the official documentation:

## Reject TURN relaying from/to the following addresses/networks:
blacklist:                 # This is the default blacklist.
    - "127.0.0.0/8"        # IPv4 loopback.
    - "::1"                # IPv6 loopback.
    - recommended          # Expands to a number of networks recommended to be
                           # blocked, but includes private networks. Those
                           # would have to be 'whitelist'ed if eturnal serves
                           # local clients/peers within such networks.

To whitelist IP addresses or specific (private) networks, you need to add a whitelist part into the configuration file, e.g.:

whitelist:
    - "192.168.0.0/16"
    - "203.0.113.113"
    - "2001:db8::/64"

The more specific, the better.

TURNS (TURN via TLS/DTLS)

Also consider supporting TLS/DTLS. To do this, adjust the following settings in the eturnal.yml configuration file (TLS parts should not be commented anymore):
```
listen:
    - ip: "::"
      port: 3478
      transport: udp
    - ip: "::"
      port: 3478
      transport: tcp
    - ip: "::"
      port: 5349
      transport: tls

## TLS certificate/key files (must be readable by 'eturnal' user!):
tls_crt_file: /etc/eturnal/tls/crt.pem
tls_key_file: /etc/eturnal/tls/key.pem
```
In this case, replace the turn: schemes in homeserver's turn_uris settings with turns:. More is described here.

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 issues as well as the underlying WebRTC issue. Consider using a ZeroSSL certificate for your TURN server as a working alternative.
Firewall

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.)
Reload/ restarting eturnal

Changes in the configuration file require eturnal to reload/ restart, this can be achieved by:
```
eturnalctl reload
```
eturnal performs a configuration check before actually reloading/ restarting and provides hints, if something is not correctly configured.

eturnalctl opterations script

eturnal offers a handy operations script which can be called e.g. to check, whether the service is up, to restart the service, to query how many active sessions exist, to change logging behaviour and so on.

Hint: If eturnalctl is not part of your $PATH, consider either sym-linking it (e.g. ´ln -s /opt/eturnal/bin/eturnalctl /usr/local/bin/eturnalctl´) or call it from the default eturnal directory directly: e.g. /opt/eturnal/bin/eturnalctl info

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