Configuring 802.1AB 802.1AB Overview
OmniSwitch AOS Release 7 Network Configuration Guide March 2011 page 10-9
LLDP Agent Operation
A network device that implements LLDP, supports an LLDP agent. An LLDP agent operates in any one of
the following three modes:
Transmit-only mode: The agent can only transmit the information about the capabilities and the current
status of the local system at regular intervals.
Receive-only mode: The agent can only receive information about the capabilities and the current status
of the remote systems.
Transmit and receive mode: The agent can transmit the capabilities and status information of the local
system and receive the capabilities and the status information of the remote system.
LLDPDU Transmission and Reception
LLDP operates in a one-way direction, so that the information in the LLDPDUs flows from one device to
another. LLDPDUs are not exchanged as an information request by one device and a response sent by
another device. The other devices do not acknowledge LLDP information received from a device.
The transmission of LLDPDU is based on two factors:
• Transmit countdown timing counter. For example, whenever the counter expires, it goes through the
entire database of ports that have links and sends the LLDPDU when the current time has exceeded the
re-transmission time interval.
• If there is change in status of any of the ports. For example, a new port is attached or a new link has
come up.
Reception of LLDPDU is a two phase process:
• LLDPDU and TLV error handling as per the 802.1AB standard
• LLDP remote system MIB update
Aging Time
The LLDP specific information of the remote system is stored in the LLDP MIB. The TTL TLV carries a
positive value in seconds, and conveys to the other device the duration for which this information is valid.
Once a remote device is learned on a local port, if the receiving device does not receive an LLDPDU from
the same remote device and on the same local port within the TTL mentioned in the previous LLDPDU,
then the local device discards the related entry from its database. This is called the aging time and can be
set by the user.
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