iputils: add ExtractMAC

1 files changed, 51 insertions, 0 deletions

diff --git a/dhcpv6/iputils.go b/dhcpv6/iputils.go
index 2b9788c..3ad157e 100644
--- a/dhcpv6/iputils.go
+++ b/dhcpv6/iputils.go
@@ -42,3 +42,54 @@ func GetGlobalAddr(ifname string) (net.IP, error) {
 		return ip.To4() == nil && ip.IsGlobalUnicast()
 	})
 }
+
+// GetMacAddressFromEUI64 will return a valid MAC address ONLY if it's a EUI-48
+func GetMacAddressFromEUI64(ip net.IP) (net.HardwareAddr, error) {
+	if ip.To16() == nil {
+		return nil, fmt.Errorf("IP address shorter than 16 bytes")
+	}
+
+	if isEUI48 := ip[11] == 0xff && ip[12] == 0xfe; !isEUI48 {
+		return nil, fmt.Errorf("IP address is not an EUI48 address")
+	}
+
+	mac := make(net.HardwareAddr, 6)
+	copy(mac[0:3], ip[8:11])
+	copy(mac[3:6], ip[13:16])
+	mac[0] ^= 0x02
+
+	return mac, nil
+}
+
+// ExtractMAC looks into the inner most PeerAddr field in the RelayInfo header
+// which contains the EUI-64 address of the client making the request, populated
+// by the dhcp relay, it is possible to extract the mac address from that IP.
+// If that fails, it looks for the MAC addressed embededded in the DUID.
+// Note that this only works with type DuidLL and DuidLLT.
+// If a mac address cannot be found an error will be returned.
+func ExtractMAC(packet DHCPv6) (net.HardwareAddr, error) {
+	msg := packet
+	if packet.IsRelay() {
+		inner, err := DecapsulateRelayIndex(packet, -1)
+		if err != nil {
+			return nil, err
+		}
+		ip := inner.(*DHCPv6Relay).PeerAddr()
+		if mac, err := GetMacAddressFromEUI64(ip); err == nil {
+			return mac, nil
+		}
+		msg, err = msg.(*DHCPv6Relay).GetInnerMessage()
+		if err != nil {
+			return nil, err
+		}
+	}
+	optclientid := msg.GetOneOption(OptionClientID)
+	if optclientid == nil {
+		return nil, fmt.Errorf("client ID not found in packet")
+	}
+	duid := optclientid.(*OptClientId).Cid
+	if duid.LinkLayerAddr == nil {
+		return nil, fmt.Errorf("failed to extract MAC")
+	}
+	return duid.LinkLayerAddr, nil
+}