# protomask
[](https://crates.io/crates/protomask)
[](https://docs.rs/protomask)
[](https://github.com/Ewpratten/protomask/actions/workflows/build.yml)
**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 packet from that source IPv6 address will be NAT-ed through its assigned IPv4 address until the reservation expires. The reverse process happens for return traffic too.
## Configuration
Protomask uses a [TOML](https://toml.io) configuration file. Here is a functional example:
```toml
[Interface]
# The IPv6 prefix to listen for V6 traffic on
Prefix = "64:ff9b::/96"
# A list of IPv4 prefixes to map V6 traffic to
Pool = ["192.0.2.0/24"]
[Rules]
# A static mapping of IPv4 and IPv6 addresses
# These addresses will not used in the dynamic pool
MapStatic = [{ v4 = "192.0.2.2", v6 = "2001:db8:1::2" }]
# How many seconds to keep a dynamic mapping alive for
ReservationDuration = 7200 # Optional
```