802.1AB Overview Configuring 802.1AB
page 13-6 OmniSwitch 6800/6850/9000 Network Configuration Guide March 2008
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 will go through the
entire database of ports that have links and send the LLDPDU if the current time has surpassed 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 remote system's LLDP specific information is stored in the LLDP MIB. The TTL TLV carries a posi-
tive value in seconds, and tells the other device as how long this information is valid. Once a remote
device is learned on a local port, if the receiving device doesn't 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 that entry from its database. This is called the aging time and can be set by the user.
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