type CallbackRouter struct {
	SetBoth  func(rcfg *Config, dcfg *dns.OSConfig) error
	SplitDNS bool

	// GetBaseConfigFunc optionally specifies a function to return the current DNS
	// config in response to GetBaseConfig.
	//
	// If nil, reading the current config isn't supported and GetBaseConfig()
	// will return ErrGetBaseConfigNotSupported.
	GetBaseConfigFunc func() (dns.OSConfig, error)

	// InitialMTU is the MTU the tun should be initialized with.
	// Zero means don't change the MTU from the default. This MTU
	// is applied only once, shortly after the TUN is created, and
	// ignored thereafter.
	InitialMTU uint32
	// contains filtered or unexported fields
}

type Config struct {
	// LocalAddrs are the address(es) for this node. This is
	// typically one IPv4/32 (the 100.x.y.z CGNAT) and one
	// IPv6/128 (Tailscale ULA).
	LocalAddrs []netip.Prefix

	// Routes are the routes that point into the Tailscale
	// interface.  These are the /32 and /128 routes to peers, as
	// well as any other subnets that peers are advertising and
	// this node has chosen to use.
	Routes []netip.Prefix

	// LocalRoutes are the routes that should not be routed through Tailscale.
	// There are no priorities set in how these routes are added, normal
	// routing rules apply.
	LocalRoutes []netip.Prefix

	// NewMTU is currently only used by the MacOS network extension
	// app to set the MTU of the tun in the router configuration
	// callback. If zero, the MTU is unchanged.
	NewMTU int

	// SubnetRoutes is the list of subnets that this node is
	// advertising to other Tailscale nodes.
	// As of 2023-10-11, this field is only used for network
	// flow logging and is otherwise ignored.
	SubnetRoutes []netip.Prefix

	// Linux-only things below, ignored on other platforms.
	SNATSubnetRoutes  bool                   // SNAT traffic to local subnets
	StatefulFiltering bool                   // Apply stateful filtering to inbound connections
	NetfilterMode     preftype.NetfilterMode // how much to manage netfilter rules
	NetfilterKind     string                 // what kind of netfilter to use (nftables, iptables)
}

type RouteTable struct {
	Name string
	Num  int
}

type Router interface {
	// Up brings the router up.
	Up() error

	// Set updates the OS network stack with a new Config. It may be
	// called multiple times with identical Configs, which the
	// implementation should handle gracefully.
	Set(*Config) error

	// UpdateMagicsockPort tells the OS network stack what port magicsock
	// is currently listening on, so it can be threaded through firewalls
	// and such. This is distinct from Set() since magicsock may rebind
	// ports independently from the Config changing.
	//
	// network should be either "udp4" or "udp6".
	UpdateMagicsockPort(port uint16, network string) error

	// Close closes the router.
	Close() error
}