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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.
LLDP packets
LLDP agents transmit information about a sending device/port in packets called LLDP Data Units
(LLDPDUs). All the LLDP information to be communicated by a device is contained within a single
1500 byte packet. A device receiving LLDP packets is not permitted to combine information from
multiple packets.
As shown in the following figure, each LLDPDU has three mandatory TLVs, an End of LLDPDU TLV,
plus optional TLVs as selected by network management.
FIGURE 5 LLDPDU packet format
Each LLDPDU consists of an untagged Ethernet header and a sequence of short, variable length
information elements known as type, length, value (TLV).
TLVs have Type, Length, and Value fields, where:
• Type identifies the kind of information being sent
• Length indicates the length (in octets) of the information string
• Value is the actual information being sent (for example, a binary bit map or an alpha-numeric string
containing one or more fields).
TLV support
This section lists the LLDP and LLDP-MED TLV support.
LLDP TLVs
There are two types of LLDP TLVs, as specified in the IEEE 802.3AB standard:
• Basic management TLVs consist of both optional general system information TLVs as well as
mandatory TLVs.
Mandatory TLVs cannot be manually configured. They are always the first three TLVs in the LLDPDU,
and are part of the packet header.
General system information TLVs are optional in LLDP implementations and are defined by the
Network Administrator.
Brocade devices support the following Basic Management TLVs:
•
‐
Chassis ID (mandatory)
‐
Port ID (mandatory)
‐
Time to Live (mandatory)
LLDP packets
178 FastIron Ethernet Switch Administration Guide
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