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WG(4) Device Drivers Manual WG(4)

wg — WireGuard pseudo-device

pseudo-device wg

The wg driver provides Virtual Private Network (VPN) interfaces for the secure exchange of layer 3 traffic with other WireGuard peers using the WireGuard protocol.

A wg interface recognises one or more peers, establishes a secure tunnel with each on demand, and tracks each peer's UDP endpoint for exchanging encrypted traffic with.

The interfaces can be created at runtime using the ifconfig wgN create command or by setting up a hostname.if(5) configuration file for netstart(8). The interface itself can be configured with ifconfig(8).

wg interfaces support the following ioctl(2)s:

struct wg_data_io *
Set the device configuration.
struct wg_data_io *
Get the device configuration.

The following glossary provides a brief overview of WireGuard terminology:

Peer
Peers exchange IPv4 or IPv6 traffic over secure tunnels. Each wg interface may be configured to recognise one or more peers.
Key
Each peer uses its private key and corresponding public key to identify itself to others. A peer configures a wg interface with its own private key and with the public keys of its peers.
Preshared key
In addition to the public keys, each peer pair may be configured with a unique pre-shared symmetric key. This is used in their handshake to guard against future compromise of the peers' encrypted tunnel if a quantum-computational attack on their Diffie-Hellman exchange becomes feasible. It is optional, but recommended.
Allowed IPs
A single wg interface may maintain concurrent tunnels connecting diverse networks. The interface therefore implements rudimentary routing and reverse-path filtering functions for its tunneled traffic. These functions reference a set of allowed IP ranges configured against each peer.

The interface will route outbound tunneled traffic to the peer configured with the most specific matching allowed IP address range, or drop it if no such match exists.

The interface will accept tunneled traffic only from the peer configured with the most specific matching allowed IP address range for the incoming traffic, or drop it if no such match exists. That is, tunneled traffic routed to a given peer cannot return through another peer of the same wg interface. This ensures that peers cannot spoof another's traffic.

Handshake
Two peers handshake to mutually authenticate each other and to establish a shared series of secret ephemeral encryption keys. Any peer may initiate a handshake. Handshakes occur only when there is traffic to send, and recur every two minutes during transfers.
Connectionless
Due to the handshake behavior, there is no connected or disconnected state.

Private keys for WireGuard can be generated from any sufficiently secure random source. The Curve25519 keys and the preshared keys are both 32 bytes long and are commonly encoded in base64 for ease of use.

Keys can be generated with openssl(1) as follows:

$ openssl rand -base64 32

Although a valid Curve25519 key must have 5 bits set to specific values, this is done by the interface and so it will accept any random 32-byte base64 string.

When an interface has a private key set with wgkey, the corresponding public key is shown in the status output of the interface:

# ifconfig wg1 | grep wgpubkey
	wgpubkey NW5l2q2MArV5ZXpVXSZwBOyqhohOf8ImDgUB+jPtJps=

Create two wg interfaces in separate rdomain(4)s, which is of no practical use but demonstrates two interfaces on the same machine:

#!/bin/sh

# create interfaces; set random private keys
ifconfig wg1 create wgport 7111 wgkey `openssl rand -base64 32` rdomain 1
ifconfig wg2 create wgport 7222 wgkey `openssl rand -base64 32` rdomain 2

# retrieve the public keys associated with the private keys
PUB1="`ifconfig wg1 | grep 'wgpubkey' | cut -d ' ' -f 2`"
PUB2="`ifconfig wg2 | grep 'wgpubkey' | cut -d ' ' -f 2`"

ifconfig wg1 wgpeer $PUB2 wgendpoint 127.0.0.1 7222 wgaip 192.168.5.2/32
ifconfig wg2 wgpeer $PUB1 wgendpoint 127.0.0.1 7111 wgaip 192.168.5.1/32
ifconfig wg1 192.168.5.1/24
ifconfig wg2 192.168.5.2/24

After this, ping one interface from the other:

$ route -T1 exec ping 192.168.5.2

The two interfaces are able to communicate through the UDP tunnel which resides in the default rdomain(4).

Show the listening sockets:

$ netstat -ln

The wg interface supports runtime debugging, which can be enabled with:

ifconfig wgN debug

Some common error messages include:

Handshake for peer X did not complete after 5 seconds, retrying
Peer X did not reply to our initiation packet, for example because:
  • The peer does not have the local interface configured as a peer. Peers must be able to mutually authenticate each other.
  • The peer endpoint IP address is incorrectly configured.
  • There are firewall rules preventing communication between hosts.
Invalid handshake initiation
The incoming handshake packet could not be processed. This is likely due to the local interface not containing the correct public key for the peer.
Invalid initiation MAC
The incoming handshake initiation packet had an invalid MAC. This is likely because the initiation sender has the wrong public key for the handshake receiver.
Packet has unallowed src IP from peer X
After decryption, an incoming data packet has a source IP address that is not assigned to the allowed IPs of Peer X.

inet(4), ip(4), netintro(4), hostname.if(5), pf.conf(5), ifconfig(8), netstart(8)

WireGuard whitepaper, https://www.wireguard.com/papers/wireguard.pdf.

The wg driver first appeared in OpenBSD 6.8.

The OpenBSD wg driver was developed by Matt Dunwoodie <[email protected]> and Jason A. Donenfeld <[email protected]>, based on code written by Jason A. Donenfeld.

March 14, 2021 OpenBSD-current