Lldp Frame Format; Lldp Operation - Cisco 6000 Series Configuration Manual

Configuring Ethernet Interfaces
These optional TLVs are automatically sent to the neighboring devices when LLDP is active, but you can
choose to disable them, using the lldp tlv-select disable command.

LLDP Frame Format

LLDP frames use the IEEE 802.3 format, which consists of these fields:
• Destination address (6 bytes)—Uses a multicast address of 01-80-C2-00-00-0E.
• Source address (6 bytes)—MAC address of the sending device or port.
• LLDP Ethertype (2 bytes)—Uses 88-CC.
• LLDP PDU (1500 bytes)—LLDP payload consisting of TLVs.
• FCS (4 bytes)—Cyclic Redundancy Check (CRC) for error checking.
LLDP TLV Format
LLDP TLVs carry the information about neighboring devices within the LLDP PDU using these basic formats:
• TLV Header (16 bits), which includes these fields:
• TLV Information String (0 to 511 bytes)

LLDP Operation

LLDP is a one-way protocol. The basic operation of LLDP consists of a sending device, which is enabled for
transmitting LLDP information, and which sends periodic advertisements of information in LLDP frames to
a receiving device.
Devices are identified using a combination of Chassis ID and Port ID TLVs to create an MSAP (MAC Service
Access Point). The receiving device saves the information about a neighbor for a certain amount of time
specified in the TTL TLV, before aging and removing the information.
LLDP supports these additional operational characteristics:
• LLDP operates independently in transmit or receive modes.
• LLDP operates as a slow protocol using only untagged frames, with transmission speeds of less than 5
• LLDP packets are sent when these events occur:
• When an LLDP frame is received, the LLDP remote services and PTOPO MIBs are updated with the
LLDP supports these actions on these TLV characteristics:
•
Interface and Hardware Component Configuration Guide for Cisco NCS 6000 Series Routers, IOS XR Release 6.4.x
• TLV Type (7 bits)
• TLV Information String Length (9 bits)
frames per second.
• The packet update frequency, specified by the lldp timer command, is reached. The default is 30.
• A change in the values of the managed objects occurs from the local system's LLDP MIB.
• LLDP is activated on an interface (3 frames are sent upon activation similar to CDP).
information in the TLVs.
• Interprets a TTL value of 0 as a request to automatically purge the information about the transmitting
device. These shutdown LLDPDUs are typically sent prior to a port becoming inoperable.
• An LLDP frame with a malformed mandatory TLV is dropped.
• A TLV with an invalid value is ignored.
• If the TTL is non-zero, copy of an unknown organizationally-specific TLV is maintained, for later
access through network management.
LLDP Frame Format
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