Management and Configuration Guide K/KA/KB.15.15

limited to reading incoming CDP packets from neighbor devices. (HP switches do not generate
CDP packets.)
Incoming CDP and LLDP packets tagged for VLAN 1 are processed even if VLAN 1 does not contain
any ports. VLAN 1 must be present, but it is typically present as the default VLAN for the switch.
NOTE: The switch may pick up CDP and LLDP multicast packets from VLAN 1 even when CDP-
and /or LLDP-enabled ports are not members of VLAN 1.
LLDP and CDP neighbor data
With both LLDP and (read-only) CDP enabled on a switch port, the port can read both LLDP and
CDP advertisements, and stores the data from both types of advertisements in its neighbor database.
(The switch stores only CDP data that has a corresponding field in the LLDP neighbor database.)
The neighbor database itself can be read by either LLDP or CDP methods or by using the show
lldp commands. Take note of the following rules and conditions:
• 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
different 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 corresponding 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 "Platform" 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 HP 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
LLDP and CDP data management 265