General Operating Principles; Operating Modes - Dell PowerConnect B-RX Configuration Manual

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General operating principles

LLDP use the services of the Data Link sublayers, Logical Link Control and Media Access Control, to
transmit and receive information to and from other LLDP Agents (protocol entities that implement
LLDP).
LLDP is a one-way protocol. An LLDP agent can transmit and receive information to and from
another LLDP agent located on an adjacent device, but it cannot solicit information from another
LLDP agent, nor can it acknowledge information received from another LLDP agent.

Operating modes

When LLDP is enabled on a global basis, by default, each port on the Brocade device will be
capable of transmitting and receiving LLDP packets. You can disable a port's ability to transmit
and receive LLDP packets, or change the operating mode to one of the following:
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Transmit mode
An LLDP agent sends LLDP packets to adjacent LLDP-enabled devices. The LLDP packets contain
information about the transmitting device and port.
An LLDP agent initiates the transmission of LLDP packets whenever the transmit countdown timing
counter expires, or whenever LLDP information has changed. When a transmit cycle is initiated,
the LLDP manager extracts the MIB objects and formats this information into TLVs. The TLVs are
inserted into an LLDPDU, addressing parameters are prepended to the LLDPDU, and the
information is sent out LLDP-enabled ports to adjacent LLDP-enabled devices.
Receive mode
An LLDP agent receives LLDP packets from adjacent LLDP-enabled devices. The LLDP packets
contain information about the transmitting device and port.
When an LLDP agent receives LLDP packets, it checks to ensure that the LLDPDUs contain the
correct sequence of mandatory TLVs, then validates optional TLVs. If the LLDP agent detects any
errors in the LLDPDUs and TLVs, it drops them in software. TLVs that are not recognized but do not
contain basic formatting errors, are assumed to be valid and are assigned a temporary
identification index and stored for future possible alter retrieval by network management. All
validated TLVs are stored in the neighbor database.
BigIron RX Series Configuration Guide
53-1001810-01
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System description can contain the device's product name or model number, version of
hardware type, and operating system
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Provides device capability, such as switch, router, or WLAN access port
Network troubleshooting:
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Information generated through LLDP can be used to detect speed and duplex mismatches
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Accurate topologies simplify troubleshooting within enterprise networks
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Can discover devices with misconfigured or unreachable IP addresses
Transmit LLDP information only
Receive LLDP information only

General operating principles

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