udp-redirect

A simple yet flexible and very fast UDP redirector. Tested on Linux x64 and MacOS / Darwin arm64.

Useful for redirecting UDP traffic (e.g., Wireguard VPN, DNS, etc.) when doing it at a different layer (e.g., from a firewall) is difficult. Does not modify the redirected packets.

Single file source code for convenience.

Community contributions are welcome.

Security

Supports enforcing the packet source for all received packets. This only provides modest security improvements as generating UDP packets is trivial.

Compile

# make

or

# gcc udp-redirect.c -o udp-redirect -Wall -O3

Run

./udp-redirect \
    --listen-port 51821 \
    --connect-host example.endpoint.net --connect-port 51822

./udp-redirect \
    --debug \
    --listen-address 192.168.1.32 --listen-port 51821 --listen-interface en0 \
        --listen-address-strict \
    --connect-host example.endpoint.net --connect-port 51822 \
        --connect-address-strict \
    --send-interface utun5 \
    --listen-sender-address 192.168.1.1 --listen-sender-port 51820

graph TD
    A["--------------------<br/>Wireguard Client<br/>--------------------<br/>Send from:<br/>---------------<br/>IP: 192.168.1.1<br/>Port: 51820"] <--> B("--------------------<br/>UDP Redirector<br/>--------------------<br/>Receive on:<br/>---------------<br/>IP: 192.168.1.32 (--listen-address) (optional)<br/>Port: 51821 (--listen-port)<br/>Interface: en0 (--listen-interface) (optional)<br/>---------------<br/>Receive from: (optional)<br/>---------------<br/>IP: 192.168.1.1 (--listen-sender-address) (optional)<br/>Port: 51820 (--listen-sender-port) (optional)<br/>Only receive from Wireguard Client (--listen-address-strict) (optional)<br/>---------------<br/>Send to:<br/>---------------<br/>Host: example.endpoint.net (--connect-host)</br>Port: 51822 (--connect-port)<br/>Only receive from Wireguard Server (--connect-address-strict) (optional)<br/>---------------<br/>Send from:<br/>---------------<br/>Interface: utun5 (--sender-interface) (optional)<br/><br/>")
    B <--> C["--------------------<br/>Wireguard Server<br/>--------------------<br/>Listen on:<br/>---------------<br/>Host: example.endpoint.net<br/>Port: 51822"]

Loading

Sample statistics output when invoked with --stats:

---- STATS 60s ----
listen:receive:packets: 7.5K (122.4 /s), listen:receive:bytes: 3.6M (59.4K/s)
listen:send:packets: 12.8K (210.2 /s), listen:send:bytes: 13.8M (225.4K/s)
connect:receive:packets: 12.8K (210.2 /s), connect:receive:bytes: 13.8M (225.4K/s)
connect:send:packets: 7.5K (122.4 /s), connect:send:bytes: 3.6M (59.4K/s)
---- STATS TOTAL ----
listen:receive:packets: 45.8K (250.0 /s), listen:receive:bytes: 13.2M (72.4K/s)
listen:send:packets: 98.3K (537.1 /s), listen:send:bytes: 122.9M (671.4K/s)
connect:receive:packets: 98.3K (537.1 /s), connect:receive:bytes: 122.9M (671.4K/s)
connect:send:packets: 45.8K (250.0 /s), connect:send:bytes: 13.2M (72.4K/s)

Documentation

Doxygen generated documentation in docs/index.html

Command Line Arguments

udp-redirect [arguments]

Runs in foreground and expects external process control (svscan, nohup, etc.)

Debug

Argument	Parameters	Req/Opt	Description
--stats		optional	Display sent/received bytes statistics every 60 seconds.
--verbose		optional	Verbose mode, can be specified multiple times.
--debug		optional	Debug mode (e.g., very verbose).
--version		optional	Display the version and exit.

Listener

The UDP sender (e.g., wireguard client) sends packets to the UDP redirector specified below.

Argument	Parameters	Req/Opt	Description
--listen-address	ipv4 address	optional	Listen address, defaults to INADDR_ANY.
--listen-port	port	required	Listen port.
--listen-interface	interface	optional	Listen interface name.
--listen-address-strict		optional	Security: By default, packets received from the connect endpoint will be sent to the source of the last packet received on the listener endpoint. In listen-address-strict mode, only accept packets from the same source as the first packet, or the source specified by listen-sender-address and listen-sender-port.

Connect

The UDP redirector sends packets to the endpoint specified below.

Argument	Parameters	Req/Opt	Description
--connect-address	ipv4 address	required	Connect address.
--connect-host	hostname	required	Connect host, overwrites connect-address if both are specified.
--connect-port	port	required	Connect port.
--connect-address-strict		optional	Security: Only accept packets from connect-host and connect-port, otherwise accept from all sources.

Sender

The UDP redirector sends packets from the local endpoint specified below. If any arguments are missing, it will be selected by the operating system (usually INADDR_ANY, random port, default interface).

Argument	Parameters	Req/Opt	Description
--send-address	ipv4 address	optional	Send packets from this address.
--send-port	port	optional	Send packets from this port.
--send-interface	interface	optional	Send packets from this interface name.

Listener security

Both must be specified; listener drops packets if they do not arrive from this address / port.

Argument	Parameters	Req/Opt	Description
--listen-sender-address	ipv4 address	optional	Listen endpoint only accepts packets from this source address.
--listen-sender-port	port	optional	Listen endpoint only accepts packets from this source port (must be set together, --listen-address-strict is implied).

Miscellaneous

Argument	Parameters	Req/Opt	Description
--ignore-errors		optional	Ignore most receive or send errors (host / network unreachable, etc.) instead of exiting. (default)
--stop-errors		optional	Stop on most receive or send errors (host / network unreachable, etc.)