H3C Technologies H3C S5120 Series Switches - Manual (Page 127)

1-3
Field Description
Source 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.
Type
The 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 type, length, and value
(TLV) sequences. Each carries a specific type of device information, as shown in Figure 1-3 .
Figure 1-3 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
TLVs are type, length, and value sequences that carry information elements. The type field identifies the
type of information, the length field measures 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 1-3 lists the basic management TLV types currently in use. Some of them must be included in
every LLDPDU.
Table 1-3 Basic LLDP TLVs
Type Description Remarks
Chassis ID Bridge MAC address of the sending device
Port ID
ID of the sending port
If the LLDPDU carries LLDP-MED TLVs, the port ID TLV
carries the MAC address of the sending port or the bridge
MAC in case the port does not have a MAC address. If the
LLDPDU carries no LLDP-MED TLVs, the port ID TLV
carries the port name.
Time To Live Life of the transmitted information on the receiving device
End of LLDPDU Marks the end of the TLV sequence in the LLDPDU
Mandatory
Port Description Port description of the sending port Optional