Configuring for Network Management Applications

LLDP (Link-Layer Discovery Protocol)

Protocol State

Packet

Inbound Data Management

Inbound Packet Forwarding

 

Generation

 

 

 

 

 

 

CDP Enabled1

n/a

Store inbound CDP data.

No forwarding of inbound

 

 

 

CDP packets.

CDP Disabled

n/a

No storage of CDP data from

 

 

neighbor devices.

Floods inbound CDP packets from connected devices to outbound ports.

LLDP Enabled1

Generatesand

Store inbound LLDP data.

No forwarding of inbound

 

transmits

 

LLDP packets.

 

LLDP packets

 

 

 

out all ports on

 

 

 

the switch.

 

 

 

 

 

 

LLDP Disabled

No packet

No storage of LLDP data

No forwarding of inbound

 

generation.

from neighbor devices.

LLDP packets.

1Both CDP data collection and LLDP transmit/receive are enabled in the default configuration. If a switch receives CDP packets and LLDP packets from the same neighbor device on the same port, it stores and displays the two types of information separately if the chassis and port ID information in the two types of advertisements is different. In this case, if you want to use only one type of data from a neighbor sending both types, disable the unwanted protocol on either the neighbor device or on the switch. However, if the chassis and port ID information in the two types of advertisements is the same, the LLDP information overwrites the CDP data for the same neighbor device on the same port.

CDP Operation and Commands

By default the switches covered in this guide have CDP enabled on each port. This is a read-only capability, meaning that the switch can receive and store information about adjacent CDP devices but does not generate CDP packets.

When a CDP-enabled switch receives a CDP packet from another CDP device, it enters that device’s data in the CDP Neighbors table, along with the port number where the data was received (and does not forward the packet). The switch also periodically purges the table of any entries that have expired. (The hold time for any data entry in the switch’s CDP Neighbors table is configured in the device transmitting the CDP packet, and cannot be controlled in the switch receiving the packet.) A switch reviews the list of CDP neighbor entries every three seconds, and purges any expired entries.

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