# protomask
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**A user space [NAT64](https://en.wikipedia.org/wiki/NAT64) implementation.**

Protomask started as a challenge to create a NAT64 implementation in a weekend. The goal of this implementation is to *keep things simple*. There aren't many knobs to tweak, so if you want to do stateful NAT or source address filtering, put something like `iptables` in front of it.

## How it works

Protomask listens on an IPv6 `/96` prefix for incoming traffic.

When traffic destined for an [embedded IPv4 address](https://datatracker.ietf.org/doc/html/rfc6052) is received, the source IPv6 address is assigned a real IPv4 address from a pool of addresses on a first-come-first-serve basis.

All further packets from that source IPv6 address will be NATed through its assigned IPv4 address until the reservation expires. The reverse of this process happens for return traffic.

Hosts that require a stable IPv4 address may be assigned a static mapping in the configuration file.

## Configuration

Protomask uses a [TOML](https://toml.io) configuration file. Here is a functional example:

```toml
# The NAT64 prefix to route to protomask
Nat64Prefix = "64:ff9b::/96"

# Optionally enable prometheus metrics on a port
Prometheus = "[::]:8080" # Optional, defaults to disabled

[Pool]
# All prefixes in the pool
Prefixes = ["192.0.2.0/24"]
# The maximum duration a prefix will be reserved for after becoming idle
MaxIdleDuration = 7200 # Optional, seconds. Defaults to 7200 (2 hours)
# Permanent address mappings
Static = [{ v4 = "192.0.2.2", v6 = "2001:db8:1::2" }]
```

## Installation

Protomask can be installed using various methods:

### Using Cargo

```bash
cargo install protomask
```

## Usage

```text
Usage: protomask [OPTIONS] <CONFIG_FILE>

Arguments:
  <CONFIG_FILE>  Path to the config file

Options:
  -v, --verbose  Enable verbose logging
  -h, --help     Print help
  -V, --version  Print version
```