LLDP Packets

LLDP (Link Layer Discovery Protocol) packets transport TLVs to other network devices (see LLDP Packet Format).

The LLDP packet contains the destination multicast address, the source MAC address, the LLDP EtherType, the LLDPDU data (which contains the TLVs), and a frame check sequence (FCS). The LLDP multicast address is defined as 01:80:C2:00:00:0E, and the EtherType is defined as 0x88CC.

LLDP Packet Format

The following characteristics apply to LLDP packets:

They are IEEE 802.3 Ethernet frames.
The frames are sent as untagged frames.
The frames are sent with a link-local-assigned multicast address as the destination address.
The STP (Spanning Tree Protocol) state of the port does not affect the transmission of LLDP frames.

The length of the packet cannot exceed 1500 bytes. As you add TLVs, you increase the length of the LLDP frame. When you reach 1500 bytes, the remaining TLVs are dropped. We recommend that you advertise information regarding only one or two VLANs on the LLDP port, to avoid dropped TLVs.

If the system drops TLVs because of exceeded length, the system logs a message to the EMS and the show lldp statistics command shows this information under the Tx Length Exceeded field.

Note

The LLDPDU maximum size is 1500 bytes, even with jumbo frames enabled. TLVs that exceed this limit are dropped.

Published March 2020prev | next

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