kubernetes/vendor/go.etcd.io/etcd/pkg/v3/netutil/routes.go

// GetDefaultHost fetches the a resolvable name that corresponds
// to the machine's default routable interface
func GetDefaultHost() (string, error) { … }

// GetDefaultInterfaces fetches the device name of default routable interface.
func GetDefaultInterfaces() (map[string]uint8, error) { … }