pktkit

Zero-copy L2/L3 packet handling toolkit for Rust.

pktkit is a feature-gated multi-tool for building virtual network topologies: devices, hubs, adapters, NAT, and tunnels that move Ethernet frames and IP packets without copying buffers on the hot path.

It is a Rust port of the Go pktkit library, re-cast into idiomatic Rust:

• Frame and Packet are #[repr(transparent)] newtypes around [u8]. You hold them as &Frame / &mut Frame, exactly like Go's []byte alias, with no per-call allocation.
• Forwarding uses synchronous callbacks (Arc<dyn Fn(&Frame) -> io::Result<()>>), not channels or async — matching the Go API one-for-one and keeping the hot path zero-cost.
• Everything beyond the core (Frame, Packet, L2Hub, L3Hub, Pipe, …) lives behind a Cargo feature so a user pulling only the core types pays nothing for crypto, OS FFI, or protocol stacks they don't use.

Features

Core (always on)

• Zero-copy types: Frame, Packet, EtherType, Protocol, MacAddr
• Traits: L2Device, L3Device, L2Acceptor, L2Connector, L3Connector
• L2Hub: MAC-learning switch with 5-minute aging
• L3Hub: prefix-routing hub with default-route fallback
• PipeL2 / PipeL3: in-memory devices for testing
• connect_l2 / connect_l3: point-to-point wiring
• serve: accept loop, with auto-cleanup on Done
• checksum: RFC 1071 + pseudo-header

Opt-in cargo features

Feature	What you get
l2adapter	ARP, NDP, gateway routing, L2Adapter bridging an L3 device onto an L2 net
dhcp	DHCP client codec + DHCPServer (DISCOVER/OFFER/REQUEST/ACK/…)
qemu	QEMU userspace network socket protocol (listener + dialer)
tuntap	TUN/TAP devices on Linux and macOS
afxdp	Linux AF_XDP zero-copy sockets
vtcp	Pure-Rust TCP engine (congestion, SACK, timestamps, window scaling, SYN cookies)
slirp	Userspace NAT stack routing virtual traffic to real sockets
vclient	High-level virtual client: dial, listen, DNS, minimal HTTP
nat	Packet-level IPv4 NAT + NAT64 + ALGs (FTP, SIP, H.323, PPTP, TFTP, IRC)
wg	WireGuard tunnel (Noise IK + transport)
ovpn	OpenVPN server (TLS control + AES-CBC/GCM data)
full	All of the above

Dependency policy

pktkit depends on:

• the Rust standard library
• libc (only when tuntap or afxdp is enabled)
• RustCrypto primitive crates (chacha20poly1305, aes-gcm, curve25519-dalek, sha2, hmac, blake2, rsa, …) — only when the relevant tunnel feature is enabled. We do not roll our own crypto.
• rustls for OpenVPN's control-channel TLS (only when ovpn is enabled), configured with a pure-Rust crypto provider (rustls-rustcrypto, backed by the same RustCrypto crates) — no ring, no aws-lc-rs, no vendored C/assembly, and no compile-time build script.

Nothing else. No async runtime. No framework. No native code beyond libc. Everything cross-compiles. The default build pulls in zero dependencies.

Usage

Point-to-point L3

Devices are shared as Arcs (the Arc<T>: L3Device blanket impl makes this ergonomic), and connect_l3 cross-wires their handlers:

use std::net::Ipv4Addr;
use std::sync::Arc;
use pktkit::{PipeL3, IpPrefix, connect_l3};

let a = Arc::new(PipeL3::new(IpPrefix::new(Ipv4Addr::new(10, 0, 0, 1).into(), 24)));
let b = Arc::new(PipeL3::new(IpPrefix::new(Ipv4Addr::new(10, 0, 0, 2).into(), 24)));
connect_l3(a, b);

Virtual LAN with DHCP and NAT

// requires: --features "l2adapter dhcp slirp"
use std::net::Ipv4Addr;
use std::sync::Arc;
use pktkit::{L2Hub, L2Adapter, L2AdapterConfig, IpPrefix, L3Device};
use pktkit::dhcp::{Server as DhcpServer, ServerConfig as DhcpConfig};
use pktkit::slirp::Stack;

let hub = Arc::new(L2Hub::new());

// DHCP server handing out 192.168.0.10–100.
let mut dcfg = DhcpConfig::new(
    Ipv4Addr::new(192, 168, 0, 1),
    Ipv4Addr::new(192, 168, 0, 10),
    Ipv4Addr::new(192, 168, 0, 100),
);
dcfg.router = Some(Ipv4Addr::new(192, 168, 0, 1));
dcfg.dns = vec![Ipv4Addr::new(1, 1, 1, 1)];
let _dhcp_handle = hub.connect(DhcpServer::new(dcfg));

// NAT gateway: a slirp stack routing to the real network, bridged onto L2.
let stack = Stack::new();
stack.set_addr(IpPrefix::new(Ipv4Addr::new(192, 168, 0, 1).into(), 24)).unwrap();
let gw = L2Adapter::new_arc(stack.clone(), L2AdapterConfig::default());
let _gw_handle = hub.connect_arc(gw);

Virtual client over the tunnel (DNS + TCP + HTTP)

// requires: --features "vclient"
use std::net::Ipv4Addr;
use pktkit::IpPrefix;
use pktkit::vclient::{Client, ClientConfig};

let client = Client::new(ClientConfig {
    prefix: Some(IpPrefix::new(Ipv4Addr::new(10, 0, 0, 2).into(), 24)),
    dns: vec![Ipv4Addr::new(1, 1, 1, 1).into()],
});
// Wire `client` into an L3 network (slirp, wg, hub) via its L3Device impl,
// then:
let resp = client.http_get("http://example.com/")?;
println!("{} {}", resp.status, resp.text());

WireGuard server with per-peer isolation

// requires: --features "wg slirp"
use std::net::{Ipv4Addr, UdpSocket};
use std::sync::Arc;
use pktkit::{IpPrefix, L3Device};
use pktkit::wg::{Adapter, AdapterConfig};
use pktkit::slirp::Stack;

let stack = Stack::new();
stack.set_addr(IpPrefix::new(Ipv4Addr::new(10, 0, 0, 1).into(), 24)).unwrap();

let adapter = Adapter::new(AdapterConfig {
    private_key,                      // your server's WireGuard private key
    multi_handler: None,
    connector: stack,                 // each peer gets isolated NAT via L3Connector
    addr: IpPrefix::new(Ipv4Addr::new(10, 0, 0, 1).into(), 24),
    on_unknown_peer: None,
})?;
adapter.add_peer(client_public_key);

let udp = UdpSocket::bind("0.0.0.0:51820")?;
adapter.serve(udp)?;

QEMU VM networking

// requires: --features "qemu"
use std::sync::Arc;
use pktkit::{L2Hub, serve};
use pktkit::qemu;

let listener = qemu::Listener::bind_unix("/tmp/qemu.sock")?;
let hub = Arc::new(L2Hub::new());
serve(&listener, &hub)?;  // accept loop: each VM joins the hub

Status

Active development; the API is not yet stable. Most features are functionally complete and tested; a few have documented // TODO(<feature>) gaps:

• ovpn: tls-crypt/tls-auth, control-packet retransmit timers, and fuller PUSH_REPLY negotiation are not yet implemented.
• afxdp: the datapath needs root + a real NIC; pure logic is unit-tested, hardware paths are marked as needing verification.
• tuntap: macOS utun is type-checked against the Apple target but not yet exercised on a macOS host.
• slirp: inbound virtual TCP accept is IPv4-only (IPv6 accept is a TODO).
• nat: SIP/H.323/PPTP ALGs rewrite payloads; UPnP's live TCP control endpoint awaits wiring through the virtual TCP listener.

License

MIT — see LICENSE.