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Figure 12 SNAP-encapsulated LLDP frame
Table 2 Fields in a SNAP-encapsulated LLDP frame
Field Description
Destination MAC address
MAC address to which the LLDP frame is advertised. It is the same as
that for Ethernet II-encapsulated LLDP frames.
Source MAC address
MAC address of the sending port.
Type
SNAP type for the upper-layer protocol. This field 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 13 LLDPDU encapsulation format
An LLDPDU can carry up to 32 types of TLVs. Mandatory TLVs include Chassis ID TLV, Port ID TLV,
and Time to Live 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 enhan ced device management.
They are defined by standardization or other organizations and are optional for LLDPDUs.
•
Basic management TLVs
lists the basic management TLV types. Some of them are mandatory for LLDPDUs.
