3Com S7902E, Руководство по настройке

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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 carrying a type of device information, as shown in Figure 1-3 .
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 Description Remarks
Chassis ID Bridge MAC address of the sending device.
Port ID
ID of the sending port.
If MED TLVs are included in the LLDPDU, 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 no MED TLVs
are included, 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