lannet

func IsCGNAT ¶

func IsCGNAT(ip net.IP) bool

IsCGNAT reports whether ip is in 100.64.0.0/10 — the shared-address range Tailscale assigns tailnet devices from. Used to tell a tailnet address apart from a physical LAN one.

func LANIP ¶

func LANIP() (net.IP, error)

LANIP returns a non-loopback IPv4 address other devices on the local network can reach this host at — the address the QR advertises so the phone can connect to the laptop's gateway and Metro.

Primary method is the UDP-dial trick: "connecting" a UDP socket to a public address makes the kernel select the egress interface (no packets are sent), and its local address is the one a peer on that path sees. Falls back to scanning interfaces for a private (RFC1918) IPv4 when the dial can't resolve a usable address (e.g. no default route).

NB: with a VPN/tailscale exit node active, the dial trick returns the tunnel address (e.g. 100.64/10) — callers that need a physical-LAN address should check IsCGNAT.

func TailnetIP ¶

func TailnetIP() net.IP

TailnetIP scans interfaces for a CGNAT (100.64/10) IPv4 — present exactly when Tailscale is up, regardless of install flavor (GUI network extension or tailscaled daemon).