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Packet boundaries in a network topology
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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-enabled.
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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.
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Any intervening 802.1D device or Layer-3 device that is either LLDP-unaware or has disabled LLDP operation
drops the packet.
LLDP operation configuration options
In the default configuration, LLDP is enabled and in both transmit and receive mode on all active ports. The LLDP
configuration includes global settings, which apply to all active ports on the switch, and per-port settings, which
affect only the operation of the specified ports.
The commands in the LLDP sections affect both LLDP and LLDP-MED operation. For information on operation
and configuration unique to LLDP-MED, see LLDP-MED (media-endpoint-discovery) on page 233.
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.
Enable or disable LLDP-MED
In the default configuration for the switches, LLDP-MED is enabled by default. (Requires that LLDP is also
enabled.) For more information, see LLDP-MED (media-endpoint-discovery) on page 233.
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.
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.
Transmit and receive mode
With LLDP enabled, the switch periodically transmits an LLDP advertisement (packet) out each active port
enabled for outbound LLDP transmissions and receives LLDP advertisements on each active port enabled to
receive LLDP traffic (Configuring per-port transmit and receive modes (CLI) on page 228). Per-port
configuration options include four modes:
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Transmit and receive (tx_rx): This is the default setting on all ports. It enables a given port to both transmit
and receive LLDP packets and to store the data from received (inbound) LLDP packets in the switch's MIB.
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Transmit only (txonly): This setting enables a port to transmit LLDP packets that can be read by LLDP
neighbors. However, the port drops inbound LLDP packets from LLDP neighbors without reading them. This
prevents the switch from learning about LLDP neighbors on that port.
Chapter 7 Configuring for Network Management Applications
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Troubleshooting
