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Warn against using Let's Encrypt certs for encrypted TURN #11686

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Jan 17, 2022
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Warn against using Let's Encrypt certs for encrypted TURN #11686

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Warn against using Let's Encrypt certs for encrypted TURN
AndrewFerr Jan 5, 2022
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Add changelog file
AndrewFerr Jan 5, 2022
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Make requested changes
AndrewFerr Jan 15, 2022
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Bring back links to Element issues
AndrewFerr Jan 17, 2022
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1 change: 1 addition & 0 deletions changelog.d/11686.doc
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Warn against using a Let's Encrypt certificate for TLS/DTLS TURN server client connections, and suggest using ZeroSSL certificate instead. This bypasses client-side connectivity errors caused by WebRTC libraries that reject Let's Encrypt certificates. Contibuted by @AndrewFerr.
14 changes: 14 additions & 0 deletions docs/turn-howto.md
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Expand Up @@ -137,6 +137,10 @@ This will install and start a systemd service called `coturn`.

# 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
Expand All @@ -145,6 +149,12 @@ This will install and start a systemd service called `coturn`.
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
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currently includes Element Android & iOS. For more details, read 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
Expand Down Expand Up @@ -250,6 +260,10 @@ Here are a few things to try:
* Check that you have opened your firewall to allow UDP traffic to the UDP
relay ports (49152-65535 by default).

* Try disabling `coturn`'s TLS/DTLS listeners and enable only its (unencrypted)
TCP/UDP listeners. (This will only leave signaling traffic unencrypted;
voice & video WebRTC traffic is always encrypted.)

* Some WebRTC implementations (notably, that of Google Chrome) appear to get
confused by TURN servers which are reachable over IPv6 (this appears to be
an unexpected side-effect of its handling of multiple IP addresses as
Expand Down