if ip = n.IP.To4(); ip == nil {
		ip = n.IP
		if len(ip) != IPv6len {
			return nil, nil
		}
	}
	m = n.Mask
	switch len(m) {
	case IPv4len:
		if len(ip) != IPv4len {
			return nil, nil
		}
	case IPv6len:
		if len(ip) == IPv4len {
			m = m[12:]
		}
	default:
		return nil, nil
	}
	return
}

// Contains reports whether the network includes ip.

		switch a.Attr.Type {
		case syscall.IFLA_ADDRESS:
			// We never return any /32 or /128 IP address
			// prefix on any IP tunnel interface as the
			// hardware address.
			switch len(a.Value) {
			case IPv4len:
				switch ifim.Type {
				case sysARPHardwareIPv4IPv4, sysARPHardwareGREIPv4, sysARPHardwareIPv6IPv4:
					continue
				}
			case IPv6len:
				switch ifim.Type {

	}
	var ifat []Addr
	for _, a := range as {
		var ip IP
		var mask IPMask
		switch a := a.(type) {
		case *lif.Inet4Addr:
			ip = IPv4(a.IP[0], a.IP[1], a.IP[2], a.IP[3])
			mask = CIDRMask(a.PrefixLen, 8*IPv4len)
		case *lif.Inet6Addr:
			ip = make(IP, IPv6len)
			copy(ip, a.IP[:])
			mask = CIDRMask(a.PrefixLen, 8*IPv6len)
		}
		ifat = append(ifat, &IPNet{IP: ip, Mask: mask})
	}
	return ifat, nil
}

			}
			prefixLen, maxPrefixLen := ifa.Mask.Size()
			if ifa.IP.To4() != nil {
				if 0 >= prefixLen || prefixLen > 8*IPv4len || maxPrefixLen != 8*IPv4len {
					return nil, fmt.Errorf("unexpected prefix length: %d/%d for %#v", prefixLen, maxPrefixLen, ifa)
				}
				if ifa.IP.IsLoopback() && prefixLen < 8 { // see RFC 1122

		for i, outkv := range out {
			if strings.HasPrefix(outkv, k) {
				out[i] = inkv
				continue NextVar
			}
		}
		out = append(out, inkv)
	}
	return out
}

const (
	IPv4len = 4
	IPv6len = 16
)

var v4InV6Prefix = []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff}

func IPv4(a, b, c, d byte) IP {
	p := make(IP, IPv6len) // ERROR "make\(IP, 16\) escapes to heap"

	case *syscall.SockaddrInet6:
		return &IPAddr{IP: sa.Addr[0:], Zone: zoneCache.name(int(sa.ZoneId))}
	}
	return nil
}

func (a *IPAddr) family() int {
	if a == nil || len(a.IP) <= IPv4len {
		return syscall.AF_INET
	}
	if a.IP.To4() != nil {
		return syscall.AF_INET
	}
	return syscall.AF_INET6
}

func (a *IPAddr) sockaddr(family int) (syscall.Sockaddr, error) {
	if a == nil {

	var ip []byte
	switch /*v4 or v6*/ {
	case s.clusterCIDR.IP.To4() != nil:
		{
			j := uint32(index) << uint32(32-s.nodeMaskSize)
			ipInt := (binary.BigEndian.Uint32(s.clusterCIDR.IP)) | j
			ip = make([]byte, net.IPv4len)
			binary.BigEndian.PutUint32(ip, ipInt)
		}
	case s.clusterCIDR.IP.To16() != nil:
		{
			// leftClusterIP      |     rightClusterIP
			// 2001:0DB8:1234:0000:0000:0000:0000:0000
			const v6NBits = 128

				return nil, errors.New("cannot parse network mask for interface: " + status)
			}
			var mask IPMask
			if ip.To4() != nil { // IPv4 or IPv6 IPv4-mapped address
				mask = CIDRMask(pfxlen-8*len(v4InV6Prefix), 8*IPv4len)
			}
			if ip.To16() != nil && ip.To4() == nil { // IPv6 address
				mask = CIDRMask(pfxlen, 8*IPv6len)
			}

			addrs = append(addrs, &IPNet{IP: ip, Mask: mask})
		}
	}

	return addrs, nil

				}
				switch sa := sa.(type) {
				case *syscall.SockaddrInet4:
					ifat = append(ifat, &IPNet{IP: IPv4(sa.Addr[0], sa.Addr[1], sa.Addr[2], sa.Addr[3]), Mask: CIDRMask(int(puni.OnLinkPrefixLength), 8*IPv4len)})
				case *syscall.SockaddrInet6:
					ifa := &IPNet{IP: make(IP, IPv6len), Mask: CIDRMask(int(puni.OnLinkPrefixLength), 8*IPv6len)}
					copy(ifa.IP, sa.Addr[:])
					ifat = append(ifat, ifa)
				}
			}

	}
	if b[2] != 0 {
		return nil, errors.New("non-zero reserved field")
	}
	l := 2
	var a socksAddr
	switch b[3] {
	case socksAddrTypeIPv4:
		l += net.IPv4len
		a.IP = make(net.IP, net.IPv4len)
	case socksAddrTypeIPv6:
		l += net.IPv6len
		a.IP = make(net.IP, net.IPv6len)
	case socksAddrTypeFQDN:
		if _, err := io.ReadFull(c, b[:1]); err != nil {
			return nil, err
		}