KB.15.15

LLDP packet forwarding

An 802.1D-compliant switch does not forward LLDP packets, regardless of whether LLDP is globally

enabled or disabled on the switch.

One IP address advertisement per port

LLDP advertises only one IP address per port, even if multiple IP addresses are configured by lldp

config <port-list> ipAddrEnable (see syntax (page 224)) on a given port.

802.1Q VLAN Information

LLDP packets do not include 802.1Q header information and are always handled as untagged

packets.

Effect of 802.1X Operation

If 802.1X port security is enabled on a port, and a connected device is not authorized, LLDP

packets are not transmitted or received on that port. Any neighbor data stored in the neighbor

MIB for that port prior to the unauthorized device connection remains in the MIB until it ages out.

If an unauthorized device later becomes authorized, LLDP transmit and receive operation resumes.

Disconnecting a neighbor LLDP device

After disconnecting a neighbor LLDP device from the switch, the neighbor can continue to appear

in the switch's neighbor database for an extended period if the neighbor's holdtime-multiplier

is high; especially if the refresh-interval is large. See “Changing the time-to-live for transmitted

advertisements” (page 221).

Mandatory TLVs

All mandatory TLVs required for LLDP operation are also mandatory for LLDP-MED operation.

Enabling topology change notification

Enabling topology change notification on a switch port and then connecting or disconnecting an

LLDP-MED endpoint on that port causes the switch to send an SNMP trap to notify the designated

management stations. The port number included in the trap corresponds to the internal number the

switch maintains for the designated port, and not the port's external (slot/number) identity. To

match the port's external slot/number to the internal port number appearing in an SNMP trap, use

the walkmib ifDescr command, as shown in Figure 121 (page 264).

Figure 121 Matching internal port numbers to external slot/port numbers

LLDP and CDP data management

This section describes points to note regarding LLDP and CDP (Cisco Discovery Protocol) data

received by the switch from other devices. LLDP operation includes both transmitting LLDP packets

to neighbor devices and reading LLDP packets received from neighbor devices. CDP operation is

264 Configuring for Network Management Applications