Configuring for Network Management Applications
LLDP (Link-Layer Discovery Protocol)
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).
Note Ports can also be enabled for reading CDP packets and storing the CDP data
in an LLDP-compatible version. See “LLDP and CDP Data Management” on
page 13-54 for details.
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-capable.
■ 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.
LLDP Configuration Options
Enable or Disable LLDP on the Switch. In the default configuration,
LLDP is globally enabled on the switch. To prevent transmission or receipt of
LLDP traffic, you can disable LLDP operation (page 13-38).
Change the Frequency of LLDP Packet Transmission to Neighbor
Devices. On a global basis, you can increase or decrease the frequency of
outbound LLDP advertisements (page 13-39).
Change the Time-To-Live for LLDP Packets Sent to Neighbors. On a
global basis, you can increase or decrease the time that the information in an
LLDP packet outbound from the switch will be maintained in a neighbor LLDP
device (page 13-39).
13-31
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