Method Start

wgengine/netstack/netstack.go:633–656

Start sets up all the handlers so netstack can start working. Implements wgengine.FakeImpl. The provided LocalBackend interface can be either nil, for special case users of netstack that don't have a LocalBackend, or a non-nil *ipnlocal.LocalBackend. Any other type will cause Start to panic. Start

(b LocalBackend)

// Start currently (2026-03-11) never returns a non-nil error, but maybe it did
// in the past and maybe it will in the future.
func (ns *Impl) Start(b LocalBackend) error {
	switch b := b.(type) {
	case nil:
		// No backend, so just continue with ns.lb unset.
	case *ipnlocal.LocalBackend:
		if b == nil {
			panic("nil LocalBackend")
		}
		ns.lb = b
	default:
		panic(fmt.Sprintf("unexpected type for LocalBackend: %T", b))
	}
	tcpFwd := tcp.NewForwarder(ns.ipstack, tcpRXBufDefSize, maxInFlightConnectionAttempts(), ns.acceptTCP)
	udpFwd := udp.NewForwarder(ns.ipstack, ns.acceptUDPNoICMP)
	ns.ipstack.SetTransportProtocolHandler(tcp.ProtocolNumber, ns.wrapTCPProtocolHandler(tcpFwd.HandlePacket))
	ns.ipstack.SetTransportProtocolHandler(udp.ProtocolNumber, ns.wrapUDPProtocolHandler(udpFwd.HandlePacket))
	ns.injectWG.Go(func() {
		ns.inject()
	})
	if ns.ready.Swap(true) {
		panic("already started")
	}
	return nil
}

func (ns *Impl) addSubnetAddress(ip netip.Addr) {
	ns.mu.Lock()