H3C Technologies H3C S12500-X Series Switches - Manual (Page 165)

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Table 12 Fields in a SNAP-encapsulated LLDPDU
Field Description
Destination MAC address
MAC address to which the LLDPDU is advertised. It is the same as that for
Ethernet II-encapsulated LLDPDUs.
Source MAC address MAC address of the sending port.
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 TLV sequences. Each TLV
carries a type of device information, as shown in Figure 51 .
Figure 51 LLDPDU encapsulation format
An LLDPDU can carry up to 32 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.
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 enhanced device management; they are defined by standardization or other
organizations and are optional to LLDPDUs.
1. Basic management TLVs
Table 13 lists the basic management TLV types. Some of them are mandatory to LLDPDUs (they
must be included in every LLDPDU).
Table 13 Basic management TLVs
Type Description Remarks
Chassis ID Specifies the bridge MAC address of the sending device.
Mandatory.
Port ID
Specifies the ID of the sending port.
If the LLDPDU carries LLDP-MED TLVs, the port ID TLV carries
the MAC address of the sending port. Otherwise, the port ID
TLV carries the port name.
Time to Live
Specifies the life of the transmitted information on the
receiving device.