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Configuring for Network Management Applications
LLDP (Link-Layer Discovery Protocol)
■ If the switch receives both LLDP and CDP advertisements on the same
port from the same neighbor the switch stores this information as two
separate entries if the advertisements have differences chassis ID and port
ID information.
■ If the chassis and port ID information are the same, the switch stores this
information as a single entry. That is, LLDP data overwrites the corre-
sponding CDP data in the neighbor database if the chassis and port ID
information in the LLDP and CDP advertisements received from the same
device is the same.
■ Data read from a CDP packet does not support some LLDP fields, such as
“System Descr”, “SystemCapSupported”, and “ChassisType”. For such
fields, LLDP assigns relevant default values. Also:
• The LLDP “System Descr” field maps to CDP’s “Version” and “Plat-
form” fields.
• The switch assigns “ChassisType” and “PortType” fields as “local” for
both the LLDP and the CDP advertisements it receives.
• Both LLDP and CDP support the “System Capability” TLV. However,
LLDP differentiates between what a device is capable of supporting
and what it is actually supporting, and separates the two types of
information into subelements of the System Capability TLV. CDP has
only a single field for this data. Thus, when CDP System Capability
data is mapped to LLDP, the same value appears in both LLDP System
Capability fields.
• System Name and Port Descr are not communicated by CDP, and thus
are not included in the switch’s Neighbors database.
Note Because ProCurve switches do not generate CDP packets, they are not
represented in the CDP data collected by any neighbor devices running CDP.
A switch with CDP disabled forwards the CDP packets it receives from other
devices, but does not store the CDP information from these packets in its own
MIB.
LLDP data transmission/collection and CDP data collection are both enabled
in the switch’s default configuration. In this state, an SNMP network
management application designed to discover devices running either CDP or
LLDP can retrieve neighbor information from the switch regardless of whether
LLDP or CDP is used to collect the device-specific information.
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