Layer 2 Discovery or Physical Connectivity Discovery

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Discovery detects the physical connections, known as Layer 2, between network devices and between network devices and other components, such a servers, and stores this data for use by Dependency Views (BSM).

How Layer 2 Discovery Works

Discovery uses multiple probes to gather information about network adapters and their Layer 2 connections.

If Discovery finds a switch in a network, it triggers the SNMP - Switch - VLAN probe and the SNMP - Network - ARPTable probe. For every VLAN Discovery finds, it triggers the switch probes. If the switch has routing capabilities, Discovery triggers the SNMP - Routing probe to collect network adapter information. If Discovery finds a server, it triggers the appropriate Address Resolution Protocol (ARP) probe for that operating system.

During the discovery of a network device, the system creates records in the Router Interface [dscy_router_interface] table containing adapter information for that device. For SNMP-enabled devices, the information is gathered from a routing probe during the exploration phase. The Layer 2 protocol cache probe runs next to collect neighbor data from the device.

As Discovery gathers network information from the probes on a device, it populates the Device Neighbors [discovery_device_neighbors] table. In some cases, the neighbors of this device might not yet be known to the instance.

The neighbor's interface cannot be resolved to a record until Discovery eventually finds the neighbor's side of the relationship. When Discovery runs on the neighboring device, Discovery completes the information for the neighbor's interface for the original reporting device.