diff --git a/vendor/github.com/google/gopacket/layers/cdp.go b/vendor/github.com/google/gopacket/layers/cdp.go
new file mode 100644
index 0000000..095f926
--- /dev/null
+++ b/vendor/github.com/google/gopacket/layers/cdp.go
@@ -0,0 +1,659 @@
+// Copyright 2012 Google, Inc. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the LICENSE file in the root of the source
+// tree.
+
+// Enum types courtesy of...
+//   http://search.cpan.org/~mchapman/Net-CDP-0.09/lib/Net/CDP.pm
+//   https://code.google.com/p/ladvd/
+//   http://anonsvn.wireshark.org/viewvc/releases/wireshark-1.8.6/epan/dissectors/packet-cdp.c
+
+package layers
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"net"
+
+	"github.com/google/gopacket"
+)
+
+// CDPTLVType is the type of each TLV value in a CiscoDiscovery packet.
+type CDPTLVType uint16
+
+// CDPTLVType values.
+const (
+	CDPTLVDevID              CDPTLVType = 0x0001
+	CDPTLVAddress            CDPTLVType = 0x0002
+	CDPTLVPortID             CDPTLVType = 0x0003
+	CDPTLVCapabilities       CDPTLVType = 0x0004
+	CDPTLVVersion            CDPTLVType = 0x0005
+	CDPTLVPlatform           CDPTLVType = 0x0006
+	CDPTLVIPPrefix           CDPTLVType = 0x0007
+	CDPTLVHello              CDPTLVType = 0x0008
+	CDPTLVVTPDomain          CDPTLVType = 0x0009
+	CDPTLVNativeVLAN         CDPTLVType = 0x000a
+	CDPTLVFullDuplex         CDPTLVType = 0x000b
+	CDPTLVVLANReply          CDPTLVType = 0x000e
+	CDPTLVVLANQuery          CDPTLVType = 0x000f
+	CDPTLVPower              CDPTLVType = 0x0010
+	CDPTLVMTU                CDPTLVType = 0x0011
+	CDPTLVExtendedTrust      CDPTLVType = 0x0012
+	CDPTLVUntrustedCOS       CDPTLVType = 0x0013
+	CDPTLVSysName            CDPTLVType = 0x0014
+	CDPTLVSysOID             CDPTLVType = 0x0015
+	CDPTLVMgmtAddresses      CDPTLVType = 0x0016
+	CDPTLVLocation           CDPTLVType = 0x0017
+	CDPTLVExternalPortID     CDPTLVType = 0x0018
+	CDPTLVPowerRequested     CDPTLVType = 0x0019
+	CDPTLVPowerAvailable     CDPTLVType = 0x001a
+	CDPTLVPortUnidirectional CDPTLVType = 0x001b
+	CDPTLVEnergyWise         CDPTLVType = 0x001d
+	CDPTLVSparePairPOE       CDPTLVType = 0x001f
+)
+
+// CiscoDiscoveryValue is a TLV value inside a CiscoDiscovery packet layer.
+type CiscoDiscoveryValue struct {
+	Type   CDPTLVType
+	Length uint16
+	Value  []byte
+}
+
+// CiscoDiscovery is a packet layer containing the Cisco Discovery Protocol.
+// See http://www.cisco.com/univercd/cc/td/doc/product/lan/trsrb/frames.htm#31885
+type CiscoDiscovery struct {
+	BaseLayer
+	Version  byte
+	TTL      byte
+	Checksum uint16
+	Values   []CiscoDiscoveryValue
+}
+
+// CDPCapability is the set of capabilities advertised by a CDP device.
+type CDPCapability uint32
+
+// CDPCapability values.
+const (
+	CDPCapMaskRouter     CDPCapability = 0x0001
+	CDPCapMaskTBBridge   CDPCapability = 0x0002
+	CDPCapMaskSPBridge   CDPCapability = 0x0004
+	CDPCapMaskSwitch     CDPCapability = 0x0008
+	CDPCapMaskHost       CDPCapability = 0x0010
+	CDPCapMaskIGMPFilter CDPCapability = 0x0020
+	CDPCapMaskRepeater   CDPCapability = 0x0040
+	CDPCapMaskPhone      CDPCapability = 0x0080
+	CDPCapMaskRemote     CDPCapability = 0x0100
+)
+
+// CDPCapabilities represents the capabilities of a device
+type CDPCapabilities struct {
+	L3Router        bool
+	TBBridge        bool
+	SPBridge        bool
+	L2Switch        bool
+	IsHost          bool
+	IGMPFilter      bool
+	L1Repeater      bool
+	IsPhone         bool
+	RemotelyManaged bool
+}
+
+// CDP Power-over-Ethernet values.
+const (
+	CDPPoEFourWire  byte = 0x01
+	CDPPoEPDArch    byte = 0x02
+	CDPPoEPDRequest byte = 0x04
+	CDPPoEPSE       byte = 0x08
+)
+
+// CDPSparePairPoE provides information on PoE.
+type CDPSparePairPoE struct {
+	PSEFourWire  bool // Supported / Not supported
+	PDArchShared bool // Shared / Independent
+	PDRequestOn  bool // On / Off
+	PSEOn        bool // On / Off
+}
+
+// CDPVLANDialogue encapsulates a VLAN Query/Reply
+type CDPVLANDialogue struct {
+	ID   uint8
+	VLAN uint16
+}
+
+// CDPPowerDialogue encapsulates a Power Query/Reply
+type CDPPowerDialogue struct {
+	ID     uint16
+	MgmtID uint16
+	Values []uint32
+}
+
+// CDPLocation provides location information for a CDP device.
+type CDPLocation struct {
+	Type     uint8 // Undocumented
+	Location string
+}
+
+// CDPHello is a Cisco Hello message (undocumented, hence the "Unknown" fields)
+type CDPHello struct {
+	OUI              []byte
+	ProtocolID       uint16
+	ClusterMaster    net.IP
+	Unknown1         net.IP
+	Version          byte
+	SubVersion       byte
+	Status           byte
+	Unknown2         byte
+	ClusterCommander net.HardwareAddr
+	SwitchMAC        net.HardwareAddr
+	Unknown3         byte
+	ManagementVLAN   uint16
+}
+
+// CDPEnergyWiseSubtype is used within CDP to define TLV values.
+type CDPEnergyWiseSubtype uint32
+
+// CDPEnergyWiseSubtype values.
+const (
+	CDPEnergyWiseRole    CDPEnergyWiseSubtype = 0x00000007
+	CDPEnergyWiseDomain  CDPEnergyWiseSubtype = 0x00000008
+	CDPEnergyWiseName    CDPEnergyWiseSubtype = 0x00000009
+	CDPEnergyWiseReplyTo CDPEnergyWiseSubtype = 0x00000017
+)
+
+// CDPEnergyWise is used by CDP to monitor and control power usage.
+type CDPEnergyWise struct {
+	EncryptedData  []byte
+	Unknown1       uint32
+	SequenceNumber uint32
+	ModelNumber    string
+	Unknown2       uint16
+	HardwareID     string
+	SerialNum      string
+	Unknown3       []byte
+	Role           string
+	Domain         string
+	Name           string
+	ReplyUnknown1  []byte
+	ReplyPort      []byte
+	ReplyAddress   []byte
+	ReplyUnknown2  []byte
+	ReplyUnknown3  []byte
+}
+
+// CiscoDiscoveryInfo represents the decoded details for a set of CiscoDiscoveryValues
+type CiscoDiscoveryInfo struct {
+	BaseLayer
+	CDPHello
+	DeviceID         string
+	Addresses        []net.IP
+	PortID           string
+	Capabilities     CDPCapabilities
+	Version          string
+	Platform         string
+	IPPrefixes       []net.IPNet
+	VTPDomain        string
+	NativeVLAN       uint16
+	FullDuplex       bool
+	VLANReply        CDPVLANDialogue
+	VLANQuery        CDPVLANDialogue
+	PowerConsumption uint16
+	MTU              uint32
+	ExtendedTrust    uint8
+	UntrustedCOS     uint8
+	SysName          string
+	SysOID           string
+	MgmtAddresses    []net.IP
+	Location         CDPLocation
+	PowerRequest     CDPPowerDialogue
+	PowerAvailable   CDPPowerDialogue
+	SparePairPoe     CDPSparePairPoE
+	EnergyWise       CDPEnergyWise
+	Unknown          []CiscoDiscoveryValue
+}
+
+// LayerType returns gopacket.LayerTypeCiscoDiscovery.
+func (c *CiscoDiscovery) LayerType() gopacket.LayerType {
+	return LayerTypeCiscoDiscovery
+}
+
+func decodeCiscoDiscovery(data []byte, p gopacket.PacketBuilder) error {
+	c := &CiscoDiscovery{
+		Version:  data[0],
+		TTL:      data[1],
+		Checksum: binary.BigEndian.Uint16(data[2:4]),
+	}
+	if c.Version != 1 && c.Version != 2 {
+		return fmt.Errorf("Invalid CiscoDiscovery version number %d", c.Version)
+	}
+	var err error
+	c.Values, err = decodeCiscoDiscoveryTLVs(data[4:], p)
+	if err != nil {
+		return err
+	}
+	c.Contents = data[0:4]
+	c.Payload = data[4:]
+	p.AddLayer(c)
+	return p.NextDecoder(gopacket.DecodeFunc(decodeCiscoDiscoveryInfo))
+}
+
+// LayerType returns gopacket.LayerTypeCiscoDiscoveryInfo.
+func (c *CiscoDiscoveryInfo) LayerType() gopacket.LayerType {
+	return LayerTypeCiscoDiscoveryInfo
+}
+
+func decodeCiscoDiscoveryTLVs(data []byte, p gopacket.PacketBuilder) (values []CiscoDiscoveryValue, err error) {
+	for len(data) > 0 {
+		if len(data) < 4 {
+			p.SetTruncated()
+			return nil, errors.New("CDP TLV < 4 bytes")
+		}
+		val := CiscoDiscoveryValue{
+			Type:   CDPTLVType(binary.BigEndian.Uint16(data[:2])),
+			Length: binary.BigEndian.Uint16(data[2:4]),
+		}
+		if val.Length < 4 {
+			err = fmt.Errorf("Invalid CiscoDiscovery value length %d", val.Length)
+			break
+		} else if len(data) < int(val.Length) {
+			p.SetTruncated()
+			return nil, fmt.Errorf("CDP TLV < length %d", val.Length)
+		}
+		val.Value = data[4:val.Length]
+		values = append(values, val)
+		data = data[val.Length:]
+	}
+	return
+}
+
+func decodeCiscoDiscoveryInfo(data []byte, p gopacket.PacketBuilder) error {
+	var err error
+	info := &CiscoDiscoveryInfo{BaseLayer: BaseLayer{Contents: data}}
+	p.AddLayer(info)
+	values, err := decodeCiscoDiscoveryTLVs(data, p)
+	if err != nil { // Unlikely, as parent decode will fail, but better safe...
+		return err
+	}
+	for _, val := range values {
+		switch val.Type {
+		case CDPTLVDevID:
+			info.DeviceID = string(val.Value)
+		case CDPTLVAddress:
+			if err = checkCDPTLVLen(val, 4); err != nil {
+				return err
+			}
+			info.Addresses, err = decodeAddresses(val.Value)
+			if err != nil {
+				return err
+			}
+		case CDPTLVPortID:
+			info.PortID = string(val.Value)
+		case CDPTLVCapabilities:
+			if err = checkCDPTLVLen(val, 4); err != nil {
+				return err
+			}
+			val := CDPCapability(binary.BigEndian.Uint32(val.Value[0:4]))
+			info.Capabilities.L3Router = (val&CDPCapMaskRouter > 0)
+			info.Capabilities.TBBridge = (val&CDPCapMaskTBBridge > 0)
+			info.Capabilities.SPBridge = (val&CDPCapMaskSPBridge > 0)
+			info.Capabilities.L2Switch = (val&CDPCapMaskSwitch > 0)
+			info.Capabilities.IsHost = (val&CDPCapMaskHost > 0)
+			info.Capabilities.IGMPFilter = (val&CDPCapMaskIGMPFilter > 0)
+			info.Capabilities.L1Repeater = (val&CDPCapMaskRepeater > 0)
+			info.Capabilities.IsPhone = (val&CDPCapMaskPhone > 0)
+			info.Capabilities.RemotelyManaged = (val&CDPCapMaskRemote > 0)
+		case CDPTLVVersion:
+			info.Version = string(val.Value)
+		case CDPTLVPlatform:
+			info.Platform = string(val.Value)
+		case CDPTLVIPPrefix:
+			v := val.Value
+			l := len(v)
+			if l%5 == 0 && l >= 5 {
+				for len(v) > 0 {
+					_, ipnet, _ := net.ParseCIDR(fmt.Sprintf("%d.%d.%d.%d/%d", v[0], v[1], v[2], v[3], v[4]))
+					info.IPPrefixes = append(info.IPPrefixes, *ipnet)
+					v = v[5:]
+				}
+			} else {
+				return fmt.Errorf("Invalid TLV %v length %d", val.Type, len(val.Value))
+			}
+		case CDPTLVHello:
+			if err = checkCDPTLVLen(val, 32); err != nil {
+				return err
+			}
+			v := val.Value
+			info.CDPHello.OUI = v[0:3]
+			info.CDPHello.ProtocolID = binary.BigEndian.Uint16(v[3:5])
+			info.CDPHello.ClusterMaster = v[5:9]
+			info.CDPHello.Unknown1 = v[9:13]
+			info.CDPHello.Version = v[13]
+			info.CDPHello.SubVersion = v[14]
+			info.CDPHello.Status = v[15]
+			info.CDPHello.Unknown2 = v[16]
+			info.CDPHello.ClusterCommander = v[17:23]
+			info.CDPHello.SwitchMAC = v[23:29]
+			info.CDPHello.Unknown3 = v[29]
+			info.CDPHello.ManagementVLAN = binary.BigEndian.Uint16(v[30:32])
+		case CDPTLVVTPDomain:
+			info.VTPDomain = string(val.Value)
+		case CDPTLVNativeVLAN:
+			if err = checkCDPTLVLen(val, 2); err != nil {
+				return err
+			}
+			info.NativeVLAN = binary.BigEndian.Uint16(val.Value[0:2])
+		case CDPTLVFullDuplex:
+			if err = checkCDPTLVLen(val, 1); err != nil {
+				return err
+			}
+			info.FullDuplex = (val.Value[0] == 1)
+		case CDPTLVVLANReply:
+			if err = checkCDPTLVLen(val, 3); err != nil {
+				return err
+			}
+			info.VLANReply.ID = uint8(val.Value[0])
+			info.VLANReply.VLAN = binary.BigEndian.Uint16(val.Value[1:3])
+		case CDPTLVVLANQuery:
+			if err = checkCDPTLVLen(val, 3); err != nil {
+				return err
+			}
+			info.VLANQuery.ID = uint8(val.Value[0])
+			info.VLANQuery.VLAN = binary.BigEndian.Uint16(val.Value[1:3])
+		case CDPTLVPower:
+			if err = checkCDPTLVLen(val, 2); err != nil {
+				return err
+			}
+			info.PowerConsumption = binary.BigEndian.Uint16(val.Value[0:2])
+		case CDPTLVMTU:
+			if err = checkCDPTLVLen(val, 4); err != nil {
+				return err
+			}
+			info.MTU = binary.BigEndian.Uint32(val.Value[0:4])
+		case CDPTLVExtendedTrust:
+			if err = checkCDPTLVLen(val, 1); err != nil {
+				return err
+			}
+			info.ExtendedTrust = uint8(val.Value[0])
+		case CDPTLVUntrustedCOS:
+			if err = checkCDPTLVLen(val, 1); err != nil {
+				return err
+			}
+			info.UntrustedCOS = uint8(val.Value[0])
+		case CDPTLVSysName:
+			info.SysName = string(val.Value)
+		case CDPTLVSysOID:
+			info.SysOID = string(val.Value)
+		case CDPTLVMgmtAddresses:
+			if err = checkCDPTLVLen(val, 4); err != nil {
+				return err
+			}
+			info.MgmtAddresses, err = decodeAddresses(val.Value)
+			if err != nil {
+				return err
+			}
+		case CDPTLVLocation:
+			if err = checkCDPTLVLen(val, 2); err != nil {
+				return err
+			}
+			info.Location.Type = uint8(val.Value[0])
+			info.Location.Location = string(val.Value[1:])
+
+			//		case CDPTLVLExternalPortID:
+			//			Undocumented
+		case CDPTLVPowerRequested:
+			if err = checkCDPTLVLen(val, 4); err != nil {
+				return err
+			}
+			info.PowerRequest.ID = binary.BigEndian.Uint16(val.Value[0:2])
+			info.PowerRequest.MgmtID = binary.BigEndian.Uint16(val.Value[2:4])
+			for n := 4; n < len(val.Value); n += 4 {
+				info.PowerRequest.Values = append(info.PowerRequest.Values, binary.BigEndian.Uint32(val.Value[n:n+4]))
+			}
+		case CDPTLVPowerAvailable:
+			if err = checkCDPTLVLen(val, 4); err != nil {
+				return err
+			}
+			info.PowerAvailable.ID = binary.BigEndian.Uint16(val.Value[0:2])
+			info.PowerAvailable.MgmtID = binary.BigEndian.Uint16(val.Value[2:4])
+			for n := 4; n < len(val.Value); n += 4 {
+				info.PowerAvailable.Values = append(info.PowerAvailable.Values, binary.BigEndian.Uint32(val.Value[n:n+4]))
+			}
+			//		case CDPTLVPortUnidirectional
+			//			Undocumented
+		case CDPTLVEnergyWise:
+			if err = checkCDPTLVLen(val, 72); err != nil {
+				return err
+			}
+			info.EnergyWise.EncryptedData = val.Value[0:20]
+			info.EnergyWise.Unknown1 = binary.BigEndian.Uint32(val.Value[20:24])
+			info.EnergyWise.SequenceNumber = binary.BigEndian.Uint32(val.Value[24:28])
+			info.EnergyWise.ModelNumber = string(val.Value[28:44])
+			info.EnergyWise.Unknown2 = binary.BigEndian.Uint16(val.Value[44:46])
+			info.EnergyWise.HardwareID = string(val.Value[46:49])
+			info.EnergyWise.SerialNum = string(val.Value[49:60])
+			info.EnergyWise.Unknown3 = val.Value[60:68]
+			tlvLen := binary.BigEndian.Uint16(val.Value[68:70])
+			tlvNum := binary.BigEndian.Uint16(val.Value[70:72])
+			data := val.Value[72:]
+			if len(data) < int(tlvLen) {
+				return fmt.Errorf("Invalid TLV length %d vs %d", tlvLen, len(data))
+			}
+			numSeen := 0
+			for len(data) > 8 {
+				numSeen++
+				if numSeen > int(tlvNum) { // Too many TLV's ?
+					return fmt.Errorf("Too many TLV's - wanted %d, saw %d", tlvNum, numSeen)
+				}
+				tType := CDPEnergyWiseSubtype(binary.BigEndian.Uint32(data[0:4]))
+				tLen := int(binary.BigEndian.Uint32(data[4:8]))
+				if tLen > len(data)-8 {
+					return fmt.Errorf("Invalid TLV length %d vs %d", tLen, len(data)-8)
+				}
+				data = data[8:]
+				switch tType {
+				case CDPEnergyWiseRole:
+					info.EnergyWise.Role = string(data[:])
+				case CDPEnergyWiseDomain:
+					info.EnergyWise.Domain = string(data[:])
+				case CDPEnergyWiseName:
+					info.EnergyWise.Name = string(data[:])
+				case CDPEnergyWiseReplyTo:
+					if len(data) >= 18 {
+						info.EnergyWise.ReplyUnknown1 = data[0:2]
+						info.EnergyWise.ReplyPort = data[2:4]
+						info.EnergyWise.ReplyAddress = data[4:8]
+						info.EnergyWise.ReplyUnknown2 = data[8:10]
+						info.EnergyWise.ReplyUnknown3 = data[10:14]
+					}
+				}
+				data = data[tLen:]
+			}
+		case CDPTLVSparePairPOE:
+			if err = checkCDPTLVLen(val, 1); err != nil {
+				return err
+			}
+			v := val.Value[0]
+			info.SparePairPoe.PSEFourWire = (v&CDPPoEFourWire > 0)
+			info.SparePairPoe.PDArchShared = (v&CDPPoEPDArch > 0)
+			info.SparePairPoe.PDRequestOn = (v&CDPPoEPDRequest > 0)
+			info.SparePairPoe.PSEOn = (v&CDPPoEPSE > 0)
+		default:
+			info.Unknown = append(info.Unknown, val)
+		}
+	}
+	return nil
+}
+
+// CDP Protocol Types
+const (
+	CDPProtocolTypeNLPID byte = 1
+	CDPProtocolType802_2 byte = 2
+)
+
+// CDPAddressType is used to define TLV values within CDP addresses.
+type CDPAddressType uint64
+
+// CDP Address types.
+const (
+	CDPAddressTypeCLNP      CDPAddressType = 0x81
+	CDPAddressTypeIPV4      CDPAddressType = 0xcc
+	CDPAddressTypeIPV6      CDPAddressType = 0xaaaa030000000800
+	CDPAddressTypeDECNET    CDPAddressType = 0xaaaa030000006003
+	CDPAddressTypeAPPLETALK CDPAddressType = 0xaaaa03000000809b
+	CDPAddressTypeIPX       CDPAddressType = 0xaaaa030000008137
+	CDPAddressTypeVINES     CDPAddressType = 0xaaaa0300000080c4
+	CDPAddressTypeXNS       CDPAddressType = 0xaaaa030000000600
+	CDPAddressTypeAPOLLO    CDPAddressType = 0xaaaa030000008019
+)
+
+func decodeAddresses(v []byte) (addresses []net.IP, err error) {
+	numaddr := int(binary.BigEndian.Uint32(v[0:4]))
+	if numaddr < 1 {
+		return nil, fmt.Errorf("Invalid Address TLV number %d", numaddr)
+	}
+	v = v[4:]
+	if len(v) < numaddr*8 {
+		return nil, fmt.Errorf("Invalid Address TLV length %d", len(v))
+	}
+	for i := 0; i < numaddr; i++ {
+		prottype := v[0]
+		if prottype != CDPProtocolTypeNLPID && prottype != CDPProtocolType802_2 { // invalid protocol type
+			return nil, fmt.Errorf("Invalid Address Protocol %d", prottype)
+		}
+		protlen := int(v[1])
+		if (prottype == CDPProtocolTypeNLPID && protlen != 1) ||
+			(prottype == CDPProtocolType802_2 && protlen != 3 && protlen != 8) { // invalid length
+			return nil, fmt.Errorf("Invalid Address Protocol length %d", protlen)
+		}
+		plen := make([]byte, 8)
+		copy(plen[8-protlen:], v[2:2+protlen])
+		protocol := CDPAddressType(binary.BigEndian.Uint64(plen))
+		v = v[2+protlen:]
+		addrlen := binary.BigEndian.Uint16(v[0:2])
+		ab := v[2 : 2+addrlen]
+		if protocol == CDPAddressTypeIPV4 && addrlen == 4 {
+			addresses = append(addresses, net.IPv4(ab[0], ab[1], ab[2], ab[3]))
+		} else if protocol == CDPAddressTypeIPV6 && addrlen == 16 {
+			addresses = append(addresses, net.IP(ab))
+		} else {
+			// only handle IPV4 & IPV6 for now
+		}
+		v = v[2+addrlen:]
+		if len(v) < 8 {
+			break
+		}
+	}
+	return
+}
+
+func (t CDPTLVType) String() (s string) {
+	switch t {
+	case CDPTLVDevID:
+		s = "Device ID"
+	case CDPTLVAddress:
+		s = "Addresses"
+	case CDPTLVPortID:
+		s = "Port ID"
+	case CDPTLVCapabilities:
+		s = "Capabilities"
+	case CDPTLVVersion:
+		s = "Software Version"
+	case CDPTLVPlatform:
+		s = "Platform"
+	case CDPTLVIPPrefix:
+		s = "IP Prefix"
+	case CDPTLVHello:
+		s = "Protocol Hello"
+	case CDPTLVVTPDomain:
+		s = "VTP Management Domain"
+	case CDPTLVNativeVLAN:
+		s = "Native VLAN"
+	case CDPTLVFullDuplex:
+		s = "Full Duplex"
+	case CDPTLVVLANReply:
+		s = "VoIP VLAN Reply"
+	case CDPTLVVLANQuery:
+		s = "VLANQuery"
+	case CDPTLVPower:
+		s = "Power consumption"
+	case CDPTLVMTU:
+		s = "MTU"
+	case CDPTLVExtendedTrust:
+		s = "Extended Trust Bitmap"
+	case CDPTLVUntrustedCOS:
+		s = "Untrusted Port CoS"
+	case CDPTLVSysName:
+		s = "System Name"
+	case CDPTLVSysOID:
+		s = "System OID"
+	case CDPTLVMgmtAddresses:
+		s = "Management Addresses"
+	case CDPTLVLocation:
+		s = "Location"
+	case CDPTLVExternalPortID:
+		s = "External Port ID"
+	case CDPTLVPowerRequested:
+		s = "Power Requested"
+	case CDPTLVPowerAvailable:
+		s = "Power Available"
+	case CDPTLVPortUnidirectional:
+		s = "Port Unidirectional"
+	case CDPTLVEnergyWise:
+		s = "Energy Wise"
+	case CDPTLVSparePairPOE:
+		s = "Spare Pair POE"
+	default:
+		s = "Unknown"
+	}
+	return
+}
+
+func (a CDPAddressType) String() (s string) {
+	switch a {
+	case CDPAddressTypeCLNP:
+		s = "Connectionless Network Protocol"
+	case CDPAddressTypeIPV4:
+		s = "IPv4"
+	case CDPAddressTypeIPV6:
+		s = "IPv6"
+	case CDPAddressTypeDECNET:
+		s = "DECnet Phase IV"
+	case CDPAddressTypeAPPLETALK:
+		s = "Apple Talk"
+	case CDPAddressTypeIPX:
+		s = "Novell IPX"
+	case CDPAddressTypeVINES:
+		s = "Banyan VINES"
+	case CDPAddressTypeXNS:
+		s = "Xerox Network Systems"
+	case CDPAddressTypeAPOLLO:
+		s = "Apollo"
+	default:
+		s = "Unknown"
+	}
+	return
+}
+
+func (t CDPEnergyWiseSubtype) String() (s string) {
+	switch t {
+	case CDPEnergyWiseRole:
+		s = "Role"
+	case CDPEnergyWiseDomain:
+		s = "Domain"
+	case CDPEnergyWiseName:
+		s = "Name"
+	case CDPEnergyWiseReplyTo:
+		s = "ReplyTo"
+	default:
+		s = "Unknown"
+	}
+	return
+}
+
+func checkCDPTLVLen(v CiscoDiscoveryValue, l int) (err error) {
+	if len(v.Value) < l {
+		err = fmt.Errorf("Invalid TLV %v length %d", v.Type, len(v.Value))
+	}
+	return
+}