udp-proxy-2020

README

udp-proxy-2020

A crappy UDP proxy for the year 2020 and beyond.

About

What is this for?

So I'm playing with Roon and I've got this complicated home network that throws Roon for a loop. I started debugging things and it turns out Roon sends broadcast messages to UDP/9003. My firewall/router will not forward these messages of course, because that's the right thing to do.

Unfortunately, I really want these broadcast messages to be forwarded to other VLAN/subnets on my local network. I started using udp-proxy-relay-redux which worked great at first.

But I also really like these messages forwarded over my OpenVPN connections which utilize the tun driver which is a point-to-point interface and explicity does not support broadcasts. This didn't work well with udp-proxy-relay-redux because Roon is poorly behaved and still tries sending "broadcasts" to the .255 address which are then dropped on the floor because my VPN server does not have the address x.x.x.255. Basically, on a point-to-point interface, these "broadcasts" were being treated as a packet destined to another host and rightfully ignored.

So what does this do?

Instead of using a normal UDP socket to listen for broadcast messages, udp-proxy-2020 uses libpcap to "sniff" the UDP broadcast messages. This means it can be a lot more flexible about what packets it "sees" so it can then sends them via libpcap/packet injection out all the other configured interfaces. If this makes you go "ew", well, welcome to 2020.

The good news...

I'm writing this in GoLang so at least cross compiling onto your random Linux/FreeBSD router/firewall is reasonably easy. No ugly cross-compling C or trying to install Python/Ruby and a bunch of libraries.

Also: HAHAHAHAHAHAHA! None of that is true! Needing to use libpcap means I have to cross compile using CGO because gopacket/pcapgo only supports Linux for reading & writing to (ethernet?) network interfaces.

Supported Systems

Pretty much any Unix-like system is supported because the dependcy list is only libpcap and golang. I develop on MacOS and specifically target pfSense/FreeBSD and Ubiquiti USG, EdgeRouter and DreamMachine/Pro as those are quite common among the Roon user community.

I release binaries for Linux/x86_64, Linux/MIPS64, Linux/ARM64, FreeBSD/amd64 and MacOS/x86_64.

There is also a docker image available.

Building udp-proxy-2020

If you are building for the same platform you intend to run udp-proxy-2020 then you just need to make sure you have libpcap and the necessary headers (you may need a -dev package for that) and run make or gmake as appropriate (we need GNU Make, not BSD Make).

If you need to build cross platform, then one of the following targets may help you:

• Linux on x86_64 make linux-amd64 via Docker
• Linux on MIPS64 make linux-mips64 (Linux/MIPS64 big-endian for Ubiquiti USG/EdgeRouter) via Docker
• Linux on ARM64 make linux-arm64 (Linux/ARM64 for Ubiquiti UDM/UDM Pro) via Docker
• FreeBSD 11.3 on x86_64 make freebsd (pfSense 2.4) via Vagrant & VirtualBox
• Docker make docker

You can get a full list of make targets and basic info about them by running: make help.

Usage

udp-proxy-2020 is still under heavy development. Run udp-proxy-2020 --help for a current list of command line options. Also, please note on many operating systems you will need to run it as the root user. Linux systems can optionally grant the CAP_NET_RAW capability.

Currently there are only a few flags you probaly need to worry about:

• --interface -- Specify two or more network interfaces to listen on.
• --port -- Specify one or more UDP ports to monitor.
• --debug -- Enable debugging output.

Advanced options:

• --fixed-ip -- Hardcode an @ to always send traffic to. Useful for things like OpenVPN in site-to-site mode.
• --timeout -- Number of ms for pcap timeout value. (default is 250ms)
• --cachettl -- Number of seconds to cache IPs for. (default is 90sec) This value may need to be increased if you have problems passing traffic to clients on OpenVPN tunnels if you can't use --fixed-ip because clients don't have a fixed ip.

There may be other flags of course, run ./udp-proxy-2020 --help for a full list.

Example:

udp-proxy-2020 --port 9003 --interface eth0,eth0.100,eth1,tun0 --cachettl 300

Would forward udp/9003 packets on four interfaces: eth0, eth1, VLAN100 on eth0 and tun0. Client IP's on tun0 would be remembered for 5minutes once they are learned.

Note: "learning" requires the client to send a udp/9003 message first! If your application requires a message to be sent to the client first, then you would need to specify --fixed-ip=1.2.3.4@tun0 where 1.2.3.4 is the IP address of the client on tun0.

Installation & Startup Scripts

There are now instructions and startup scripts available in the startup-scripts directory. If you figure out how to add support for another platform, please send me a pull request!

FAQ

So is it a "proxy"? Are there any proxy config settings I need to configure in my app?

Nope, it's not a proxy. It's more like a router. You don't need to make any changes other than running it on your home router/firewall.

Then why did you call it udp-proxy-2020?

Honestly, I didn't really think much about the name and this was the first thing that came to my mind.

What network interface types are supported?

• Ethernet
• WiFi interfaces which appear as Ethernet
• tun interfaces, like those used by OpenVPN
• raw interfaces, like those used by Wireguard

How can I get udp-proxy-2020 working with Wireguard on Ubiquiti USG?

So I haven't done this myself, but Bart Verhoeven over on the Roon Community forums wrote up this really detailed how to.

What binary is right for me?

udp-proxy-2020 is built for multiple OS and hardware platforms:

• MacOS/Intel x86_64: darwin-x86_64
• Linux/Intel x86_64: linux-amd64
• Linux/ARM64: linux-arm64
• Linux/ARM32EL: linux-arm32
• Linux/ARM32HF (hardware floating point): linux-arm32hf
• Linux/MIPS64: linux-mips64
• FreeBSD/Intel x86_64:: freebsd-amd64