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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