HP 6120 LLDP-MED, General LLDP Operation, Packet Boundaries in a Network Topology, TLV, (Type-Length-Value):

Configuring for Network Management Applications

LLDP (Link-Layer Discovery Protocol)

TLV (Type-Length-Value):A data unit that includes a data type field, a data unit length field (in bytes), and a field containing the actual data the unit is designed to carry (as an alphanumeric string, a bitmap, or a subgroup of information). Some TLVs include subelements that occur as separate data points in displays of information maintained by the switch for LLDP advertisements. (That is, some TLVs include multiple data points or subelements.)

General LLDP Operation

An LLDP packet contains data about the transmitting switch and port. The switch advertises itself to adjacent (neighbor) devices by transmitting LLDP data packets out all ports on which outbound LLDP is enabled, and reading LLDP advertisements from neighbor devices on ports that are inbound LLDP- enabled. (LLDP is a one-way protocol and does not include any acknowledgement mechanism.) An LLDP-enabled port receiving LLDP packets inbound from neighbor devices stores the packet data in a Neighbor database (MIB).

LLDP-MED

This capability is an extension to LLDP and is available on the switches covered in this guide. Refer to “LLDP-MED(Media-Endpoint-Discovery)” on page 13-55.

Packet Boundaries in a Network Topology

■Where multiple LLDP devices are directly connected, an outbound LLDP packet travels only to the next LLDP device. An LLDP-capable device does not forward LLDP packets to any other devices, regardless of whether they are LLDP-enabled.

■An intervening hub or repeater forwards the LLDP packets it receives in the same manner as any other multicast packets it receives. Thus, two LLDP switches joined by a hub or repeater handle LLDP traffic in the same way that they would if directly connected.

■Any intervening 802.1D device or Layer-3 device that is either LLDP- unaware or has disabled LLDP operation drops the packet.

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