General Lldp Operation - HP ProCurve 6400cl Series Management And Configuration Manual

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 acknowledge­
ment mechanism.) An LLDP-enabled port receiving LLDP packets inbound
from neighbor devices stores the packet data in a Neighbor database (MIB).
Series 3400cl and 6400cl Switches. Ports on these switches can also be
enabled for reading CDP packets and storing the CDP data in an LLDP-
compatible version. Note that if LDP and CDP advertisements from the same
neighbor on the same port use different chassis and port ID information, then
the two types of advertisements are stored as separate entries and the neigh­
bor port will be listed in the neighbor database as separate devices on the same
port. However, if LLDP and CDP advertisements from the same neighbor on
the same port use the same chassis and port ID information, then the LLDP
data will overwrite the CDP data and the neighbor database will include only
one entry for that neighbor on that port. This database can be read by LLDP-
or CDP-capable tools, as well as the 3400cl/6400cl show lldp commands. You
can control the participation of individual ports in these transactions and
specify whether certain types of information are included or withheld. (Note
that data from CDP advertisements read by 3400cl/6400cl switches may not
completely populate the remote data fields in the LLDP neighbors table for
these switches.) If duplicate device entries create a problem, you can elimi­
nate the duplication by disabling one of the discovery protocols.
Series 5300xl Switches. These switches also have CDP capability. How-
ever they do not store received CDP data in an LLDP-compatible format for
reading by the LLDP facility. For more information on CDP operation in the
5300xl switches, refer to "CDP on the Series 5300xl Switches" on page 14-53.
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-capabale 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.
Configuring for Network Management Applications
LLDP (Link-Layer Discovery Protocol)
14-27