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584 | Link Layer Discovery Protocol
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Figure 26-1. Type, Length, Value (TLV) Segment
TLVs are encapsulated in a frame called an LLDP Data Unit (LLDPDU) (Figure 26-2), which is
transmitted from one LLDP-enabled device to its LLDP-enabled neighbors. LLDP is a one-way protocol.
LLDP-enabled devices (LLDP agents) can transmit and/or receive advertisements, but they cannot solicit
and do not respond to advertisements.
There are five types of TLVs. All types are mandatory in the construction of an LLDPDU except Optional
TLVs. The inclusion of individual Optional TLVs is user configurable.
Figure 26-2. LLDPDU Frame
Table 26-1. Type, Length, Value (TLV) Types
Type TLV Description
0 End of LLDPDU Marks the end of an LLDPDU
1 Chassis ID An administratively assigned name that identifies the LLDP agent
2 Port ID An administratively assigned name that identifies a port through which TLVs are sent
and received
3 Time to Live A value that tells the receiving agent how long the information contained in the TLV
Value field is valid
— Optional Includes sub-types of TLVs that advertise specific configuration information. These
sub-types are Management TLVs, IEEE 802.1, IEEE 802.3, and TIA-1057
Organizationally Specific TLVs.
Chassis ID Sub-type
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Chassis ID
7 bits
9 bits
1 octet
1- 255 octets
TLV Type
(1-127)
TLV Length
Value
TLV Header
0-511 octets
TLV 1
Chassis ID
Preamble
Start Frame
Delimiter
Destination MAC
(01:80:C2:00:00:0E)
Source MAC
Ethernet Type
(0x88CC)
LLDPDU
Padding
FCS
TLV 2
Port ID
TLV 3
Port Description
TLV 4
System Name
TLV 5
System Description
TLV 6
System Capabilities
TLV 7
Management Addr
TLV 0
End of LLDPDU
TLV 127
Organizationally Specific
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