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173
Figure 173 LLDP frame encapsulated in SNAP
Table 70 Fields in a SNAP-encapsulated LLDP frame
Field Description
Destination MAC address
MAC address to which the LLDP frame is advertised. It is fixed to
0x0180-C200-000E, a multicast MAC address.
Source MAC address
MAC address of the sending port. If the port does not have a MAC
address, the MAC address of the sending bridge is used.
Type
SNAP type for the upper layer protocol. It is
0xAAAA-0300-0000-88CC for LLDP.
Data LLDPDU.
FCS
Frame check sequence, a 32-bit CRC value used to determine the
validity of the received Ethernet frame.
LLDPDUs
LLDP uses LLDPDUs to exchange information. An LLDPDU comprises multiple TLVs. Each TLV
carries a type of device information, as shown in
Figure 174 .
Figure 174 LLDPDU encapsulation format
An LLDPDU can carry up to 28 types of TLVs. Mandatory TLVs include Chassis ID TLV, Port ID TLV,
Time to Live TLV, and End of LLDPDU TLV. Other TLVs are optional.
TLVs
A TLV is an information element that contains the type, length, and value fields.
LLDPDU TLVs include the following categories:
•
Basic management TLVs
•
Organizationally (IEEE 802.1 and IEEE 802.3) specific TLVs
•
LLDP-MED (media endpoint discovery) TLVs
Basic management TLVs are essential to device management.
Organizationally specific TLVs and LLDP-MED TLVs are used for improved device management.
They are defined by standardization or other organizations and are optional to LLDPDUs.
•
Basic management TLVs
Table 71 lists the basic management TLV types. Some of them are mandatory for LLDPDUs.