3Com 4500G Family Configuration Manual page 122

The fields in the frame are described in
Table 1-2 Description of the fields in a SNAP-encapsulated LLDP frame
Field
Destination MAC address
Source MAC address
Type
Data
FCS
LLDPDUs
LLDP uses LLDPDUs to exchange information. An LLDPDU comprises multiple type, length, and value
(TLV) sequences, each carrying a type of device information, as shown in
Figure 1-3 An LLDPDU
An LLDPDU can carry up to 28 types of TLVs, of which the chassis ID TLV, port ID TLV, TTL TLV, and
end of LLDPDU TLV (end TLV in the figure) are mandatory TLVs that must be carried and other TLVs
are optional.
TLVs
TLVs are type, length, and value sequences that carry information elements, where the type field
identifies the type of information, the length field indicates the length of the information field in octets,
and the value field contains the information itself.
LLDPDU TLVs fall into these categories: basic management TLVs, organizationally (IEEE 802.1 and
IEEE 802.3) specific TLVs, and LLDP-MED (media endpoint discovery) TLVs. Basic management TLVs
are essential to device management. Organizationally specific TLVs and LLDP-MED TLVs are used for
enhanced device management; they are defined by standardization or other organizations and thus are
optional to LLDPDUs.
1) Basic management TLVs
Table 1-1 lists the basic management TLV types currently in use. Some of them are mandatory to
LLDPDUs, that is, must be included in every LLDPDU.
Table 1-3 Basic LLDP TLVs
Type
Chassis ID
Table 1-2:
The MAC address to which the LLDPDU is advertised. It is fixed to
0x0180-C200-000E, a multicast MAC address.
The MAC address of the sending port. If the port does not have a MAC
address, the MAC address of the sending bridge is used.
The SNAP type for the upper layer protocol. It is
0xAAAA-0300-0000-88CC for LLDP.
LLDPDU.
Frame check sequence, a 32-bit CRC value used to determine the
validity of the received Ethernet frame.
Bridge MAC address of the sending device.
1-3
Description
Description
Figure 1-3.
Remarks
Mandatory