Sunday, 5 July 2015

Link Layer Discovery Protocol (LLDP)

Link Layer Discovery Protocol (LLDP), standardized by the IEEE as part of 802.1ab, enables standardized discovery of nodes in a multivendor environment.


  • Use of LLDP is limited to 802.1 media types such as Ethernet, Token Ring, and Fiber Distributed Data Interface (FDDI) networks. It can't be used for HDLC, Frame-Relay, ATM, etc.
  • LLDP and CDP can run on the same interface

LLDP is unidirectional, operating only in an advertising mode. LLDP enabled nodes will send multicast frames out of all LLDP enabled interfaces. LLDP enabled nodes which receive LLDP frames can record information about their neighbors and build their own topology database. Each node can be configured to enable/disable send and/or receive of LLDP frames as separate task.

LLDP exchange attributes in the format of TLVs between devices to discover each other.

The switch supports these basic management TLVs. These are mandatory LLDP TLVs.
  • Port description TLV
  • System name TLV
  • System description TLV
  • System capabilities TLV
  • Management address TLV

These organizationally specific LLDP TLVs are also advertised to support LLDP-MED.

  • Port VLAN ID TLV 
  • MAC/PHY configuration/status TLV

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