"AddrPort.Port",
		"AddrPort.IsValid",
		"Prefix.IsSingleIP",
		"Prefix.Masked",
		"Prefix.IsValid",
		"PrefixFrom",
		"Prefix.Addr",
		"Prefix.Bits",
		"AddrFrom4",
		"IPv6LinkLocalAllNodes",
		"IPv6Unspecified",
		"MustParseAddr",
		"MustParseAddrPort",
		"MustParsePrefix",
		"appendDecimal",
		"appendHex",
		"uint128.addOne",
		"uint128.and",
		"uint128.bitsClearedFrom",
		"uint128.bitsSetFrom",

		resolveTCPAddrTests = append(resolveTCPAddrTests, resolveTCPAddrTest{"tcp", "[::]:4", &TCPAddr{IP: IPv6unspecified, Port: 4}, nil})
		resolveUDPAddrTests = append(resolveUDPAddrTests, resolveUDPAddrTest{"udp", "[::]:4", &UDPAddr{IP: IPv6unspecified, Port: 4}, nil})
		resolveIPAddrTests = append(resolveIPAddrTests, resolveIPAddrTest{"ip", "::", &IPAddr{IP: IPv6unspecified}, nil})
	}

	ifi := loopbackInterface()
	if ifi != nil {

	// Output:
	// true
	// false
	// true
	// false
}

func ExampleIP_IsUnspecified() {
	ipv6Unspecified := net.ParseIP("::")
	ipv6Specified := net.ParseIP("fe00::")
	ipv4Unspecified := net.ParseIP("0.0.0.0")
	ipv4Specified := net.ParseIP("8.8.8.8")

	fmt.Println(ipv6Unspecified.IsUnspecified())
	fmt.Println(ipv6Specified.IsUnspecified())
	fmt.Println(ipv4Unspecified.IsUnspecified())

	if err != nil {
		return nil, err
	}
	// Issue 18806: if the machine has halfway configured
	// IPv6 such that it can bind on "::" (IPv6unspecified)
	// but not connect back to that same address, fall
	// back to dialing 0.0.0.0.
	if len(ips) == 1 && ips[0].IP.Equal(IPv6unspecified) {
		ips = append(ips, IPAddr{IP: IPv4zero})
	}

	var filter func(IPAddr) bool
	if net != "" && net[len(net)-1] == '4' {

				return err
			}
			addr := *addr
			switch fd.family {
			case syscall.AF_INET:
				addr.IP = IPv4zero
			case syscall.AF_INET6:
				addr.IP = IPv6unspecified
			}
			laddr = &addr
		}
	}
	var err error
	var lsa syscall.Sockaddr
	if lsa, err = laddr.sockaddr(fd.family); err != nil {
		return err
	}

	if ctrlCtxFn != nil {