Brocade Communications Systems 53-1002163-02 manual Layer 2 topology mapping

9 Layer 2 topology mapping

Layer 2 topology mapping

The LLDP protocol lets network management systems accurately discover and model Layer 2 network topologies. As LLDP devices transmit and receive advertisements, the devices store information they discover about their neighbors. Advertisement data such as a neighbor's management address, device type, and port identification is useful in determining what neighboring devices are in the network.

NOTE

Brocade’s LLDP implementation supports a one-to-one connection. Each interface has one and only one neighbor.

The higher level management tools, such as Brocade’s DCFM, can query the LLDP information to draw Layer 2 physical topologies. The management tools can continue to query a neighboring device through the device’s management address provided in the LLDP information exchange. As this process is repeated, the complete Layer 2 topology is mapped.

In LLDP the link discovery is achieved through the exchange of link-level information between two link partners. The link-level information is refreshed periodically to reflect any dynamic changes in link-level parameters. The basic format for exchanging information in LLDP is in the form of a type, length, value (TLV) field.

LLDP keeps a database for both local and remote configurations. The LLDP standard currently supports three categories of TLVs. Brocade’s LLDP implementation adds a proprietary Brocade extension TLV set. The four TLV sets are described as follows:

•Basic management TLV set. This set provides information to map the Layer 2 topology and includes the following TLVs:

-Chassis ID TLV—Provides the ID for the switch or router where the port resides. This is a mandatory TLV.

-Optional TLV—Provides a description of the port in an alphanumeric format. If the LAN device supports RFC-2863, the port description TLV value equals the “ifDescr” object. This is a mandatory TLV.

-System name TLV—Provides the system-assigned name in an alphanumeric format. If the LAN device supports RFC-3418, the system name TLV value equals the “sysName” object. This is an optional TLV.

-System description TLV—Provides a description of the network entity in an alphanumeric format. This includes system name, hardware version, operating system, and supported networking software. If the LAN device supports RFC-3418, the value equals the “sysDescr” object. This is an optional TLV.

-System capabilities TLV—Indicates the primary functions of the device and whether these functions are enabled in the device. The capabilities are indicated by two octets. The first octet indicates Other, Repeater, Bridge, WLAN AP, Router, Telephone, DOCSIS cable device, and Station, respectively. The second octet is reserved. This is an optional TLV.

-Management address TLV—Indicates the addresses of the local switch. Remote switches can use this address to obtain information related to the local switch. This is an optional TLV.

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