SNI Relay

Simple SNI relay server written in Go.

What it does:

1. Provides a DNS server that can re-route domains to the SNI relay server.
2. Listens for incoming HTTP or HTTPS connections.
3. Parses the hostname from the HTTP request or TLS ClientHello.
4. Proxies the traffic further to that hostname.

Why would you need it? For instance, if you operate a DNS server, and you want to relay some domains to an intermediate server (effectively, change your IP address).

How to use it

1. Get the version for you OS/arch from the Releases page. If you prefer Docker, you can find it below.

2. Create a configuration file. Read the comments in ./config.yaml.dist to learn about configuration.

3. Run snirelay:

   snirelay -c /path/to/config.yaml

   You may need to run it with sudo since it needs to use privileged ports.

Usage

Usage:
  snirelay [OPTIONS]

Application Options:
  -c, --config-path= Path to the config file.
  -v, --verbose      Verbose output (optional).

Help Options:
  -h, --help         Show this help message

Docker

The docker image is available. In order to use it, you need to supply a configuration file, and you may need to also supply the TLS cert/key if you're going to use encrypted DNS.

The image exposes a number of ports that needs to be mapped to the host machine depending on what parts of the functionality you're using.

• Port 53: plain DNS server, usually needs to be mapped to port 53 of the host machine.
• Port 853/tcp: DNS-over-TLS server, usually needs to be mapped to port 853 of the host machine.
• Port 853/udp: DNS-over-QUIC server, usually needs to be mapped to port 853 of the host machine.
• Port 8443/tcp: DNS-over-HTTPS server. Do not expose to 443 as this port is required by the SNI relay server. Try a different port and don't forget to use it in the server address.
• Port 80/tcp: SNI relay port for plain HTTP connections. Map it to port 80 of the host machine.
• Port 443/tcp: SNI relay port for HTTPS connections. Map it to port 443 of the host machine.
• Port 8123/tcp: Prometheus metrics endpoint. Map it if you use prometheus.

So imagine we have a configuration file config.yaml and the TLS configuration files in the same directory in example.crt and example.key. In this case the configuration section should look like this:

dns:
  # ... omitted other ...
  tls-cert-path: "/app/example.crt"
  tls-key-path: "/app/example.key"
  # ... omitted other ...

And then run it like this:

docker run -d --name snirelay \
  -p 53:53/tcp -p 53:53/udp \
  -p 853:853/tcp -p 853:853/udp \
  -p 8443:8443/tcp \
  -p 8123:8123/tcp \
  -p 80:80/tcp -p 443:443/tcp \
  -v $(pwd)/config.yaml:/app/config.yaml \
  -v $(pwd)/example.crt:/app/example.crt \
  -v $(pwd)/example.key:/app/example.key \
  ghcr.io/ameshkov/snirelay

How to build

make

How to run it locally

See the config.yaml.dist for more information on what can be configured. In normal environment you want to change ports there.

./snirelay -c config.yaml

How to test

Note that instructions here use dnslookup and gocurl.

DNS queries

Plain DNS:

# IPv4 will be redirected to 127.0.0.1.
dnslookup www.google.com 127.0.0.1:5353

# IPv6 will be redirected to ::.
RRTYPE=AAAA dnslookup www.google.com 127.0.0.1:5353

# HTTPS will be suppressed.
RRTYPE=HTTPS dnslookup www.google.com 127.0.0.1:5353

Encrypted DNS:

# DNS-over-TLS.
VERIFY=0 dnslookup www.google.com tls://127.0.0.1:8853

# DNS-over-QUIC.
VERIFY=0 dnslookup www.google.com quic://127.0.0.1:8853

# DNS-over-HTTPS.
VERIFY=0 dnslookup www.google.com https://127.0.0.1:8443/dns-query

SNI relay

# Relay for plain HTTP:
gocurl --connect-to="example.org:443:127.0.0.1:9080" -I http://example.org/

# Relay for HTTPS:
gocurl --connect-to="example.org:443:127.0.0.1:9443" -I https://example.org/

# Or you can specify the DNS server:
gocurl --dns-servers "127.0.0.1:5353" -I https://example.org/