CCNA: CDP/LLDP

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Description:

Cisco Discovery Protocol (proprietary) runs only on Cisco devices; it allows you to gather information about other routers and switches. It is enabled by default. It can also be a very useful command to use while troubleshooting to see which devices are directly connected to the device you are connected to.

To disable CDP For the whole switch:

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   Router(config)#no cdp run

To disable CDP for an interface:

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   Router(config-if)#no cdp enable

Show Commands:

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   show cdp
   show cdp neighbors
   show cdp neighbors detail
   show cdp entry

Open source CDP = LLDP

  • To support non-Cisco devices and to allow for interoperability between other devices, the switch supports the IEEE 802.1AB LLDP.
  • LLDP is a neighbor discovery protocol that is used for network devices to advertise information about themselves to other devices on the network.
  • This protocol runs over the data-link layer, which allows two systems running different network layer protocols to learn about each other.
  • LLDP supports a set of attributes that it uses to discover neighbor devices.
  • These attributes contain type, length, and value descriptions and are referred to as TLVs.
  • LLDP supported devices can use TLVs to receive and send information to their neighbors.
  • Details such as configuration information, device capabilities, and device identity can be advertised using this protocol.
  • LLDP is disabled by default

To Enable LLDP globally:

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   config t
   lldp run
   end

To Enable LLDP per interface:

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   config t
   int fa0/0
   lldp transmit
   lldp receive
   end
   copy run start

LLDP Commands:

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   clear lldp counters
   clear lldp table
   show lldp
   show lldp errors

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