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dsinecos
Asked: 2020-09-09 10:13:32 +0800 CST

In WireGuard on a sending peer, how is packet sent from the `wg0` interface to the UDP port?

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I'm trying to understand, once a packet reaches the WireGuard interface (wg0) how is it sent to the UDP port from where it can be sent to the receiving peer.

I was reading the WireGuard whitepaper and it says

The interface itself has a private key and a UDP port on which it listens (more on that later), followed by a list of peers

I have only an elementary understanding of networking but I thought processes listen on ports so what does it mean for a network interface to listen on a UDP port?

If there is some way for a network interface to listen to a port, then on the receiving peer, the packet can likewise be received on the WireGuard interface from the UDP port. Is this a correct understanding?

networking wireguard packets

1 Answers

  1. WireGuard does create an UDP socket and binds it to an address with special kernel functions: sock_create_kern and kernel_bind.

    Here is WireGuard's source code for creating the IPv4 socket. There is a similar code for the IPv6 socket.

    WireGuard binds the socket to an UDP tunnel with the setup_upd_tunnel call as well.

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