How Lldp Works; Compatibility Of Lldp With Cdp - HP V1910 User Manual

Management address
The management address of a device is used by the network management system to identify and manage
the device for topology maintenance and network management. The management address is encapsulated
in the management address TLV.

How LLDP works

Operating modes of LLDP
LLDP can operate in one of the following modes:
TxRx mode. A port in this mode sends and receives LLDPDUs.

 Tx mode. A port in this mode only sends LLDPDUs.
 Rx mode. A port in this mode only receives LLDPDUs.
 Disable mode. A port in this mode does not send or receive LLDPDUs.
When the LLDP operating mode of a port changes, its LLDP protocol state machine re-initializes. A
re-initialization delay, which is user configurable, prevents LLDP from being initialized too frequently during
times of frequent operating mode change. With this delay configured, before a port can initialize LLDP, it
must wait for the specified interval after the LLDP operating mode changes.
Transmitting LLDPDUs
An LLDP-enabled port operating in TxRx mode or Tx mode sends LLDPDUs to its directly connected devices
both periodically and when the local configuration changes. A frame transmit interval between two
successive LLDP frames prevents the network from being overwhelmed by LLDPDUs during times of frequent
local device information change.
This interval is shortened to 1 second in either of the following cases:
 A new neighbor is discovered. A new LLDPDU is received carrying device information new to the local
device.
The LLDP operating mode of the port changes from Disable/Rx to TxRx or Tx.

This is the fast sending mechanism of LLDP. This feature sends a specific number of LLDPDUs at 1-second
intervals to help LLDP neighbors discover the local device as soon as possible. Then, the normal LLDPDU
transit interval resumes.
Receiving LLDPDUs
An LLDP-enabled port operating in TxRx mode or Rx mode checks the validity of TLVs carried in every
received LLDPDU. If valid, the information is saved and an aging timer is set for it based on the time to live
(TTL) value in the TTL TLV carried in the LLDPDU. If the TTL value is zero, the information is aged out
immediately.

Compatibility of LLDP with CDP

To make your device work with Cisco IP phones, you must enable CDP compatibility.
If your LLDP-enabled device cannot recognize Cisco Discovery Protocol (CDP) packets, it does not respond
to the requests of Cisco IP phones for the voice VLAN ID configured on the device. As a result, a requesting
Cisco IP phone sends voice traffic without any tag to your device, which disables your device from
differentiating the voice traffic from other types of traffic.
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