4000 Router Series Layer 2 - LAN Switching Configuration Guide

Table 8 Fields in a SNAP-encapsulated LLDPDU

Field Descri

tion

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 23.

Figure 23 LLDPDU enca

psulation 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 fall into 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 9 lists the basic management TLV types. Some of them are mandatory to LLDPDUs (they must

be included in every LLDPDU).

Table 9 Basic management TLVs

e Descri

tion

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.