Discovery identifiers

  • Release version: Yokohama
  • Updated March 24, 2026
  • 4 minutes to read
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    Summary of Discovery identifiers

    Discovery identifiers in ServiceNow are used after Discovery classifies a configuration item (CI) to determine if the device already exists in the CMDB. Identity probes collect identification data such as serial numbers, names, and network information, which is processed by identity sensors and passed to identifiers. These identifiers then either update existing CIs, create new ones, or take no action, helping prevent duplicate CIs and ensuring accurate asset tracking. This identification process occurs only for the Configuration item type of Discovery.

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    Key Features

    • Identity Probes and Sensors: Multi-probes and sensors gather detailed device information including serial numbers, network identifiers, and names for precise identification.
    • CMDB Identifier Rules: Rules are configured per CI class or table to define attributes used for identification, such as serial numbers, IP addresses, MAC addresses, and machine names.
    • Matching Strategy: Custom identifier rules can be created for specific CI classes to handle scenarios like NIC bonding by using attributes such as the device name alongside network identifiers.
    • Evaluation Order: Identifiers are processed in order based on configurable priority values, allowing customization to run before, after, or mixed with default identifiers.
    • Duplicate CI Handling: Properties like glide.identificationengine.skipduplicates control how Discovery manages duplicate CIs during identification.
    • Identifier Version Control: Upgraded instances can switch between legacy and new CMDB Identification and Reconciliation framework identifiers using a system property, with Service Mapping always enforcing the new framework.
    • Serial Number Management: Serial numbers are critical for asset tracking and are stored in the cmdbserialnumber table with types varying by CI.
    • Customization: Customers can create custom identity multi-probes and multi-sensors to extend Discovery for CIs not identified by default probes.

    Key Outcomes

    By leveraging Discovery identifiers, ServiceNow customers can reliably identify and track configuration items without duplications, ensuring the CMDB remains accurate and reflective of the actual IT environment. Accurate serial number discovery supports asset management and reconciliation processes. Customizable identifier rules and probe configurations enable adaptation to complex network scenarios and unique organizational needs. This results in improved data quality, streamlined Discovery operations, and better support for IT service management and asset tracking.

    After Discovery classifies a configuration item (CI), it uses identifiers to determine if the device already exists in the CMDB.

    Discovery launches special identity probes that accumulate identification data for each device and feed that data into the identifiers, which determine the action that Discovery must take for each device. Identifiers accurately determine the identity of the device to avoid the creation of duplicate CIs. This identification step only takes place for the Configuration item type of discovery, not for the other types of discovery.

    The identity probe in the base Discovery system can be configured to ask the device for information such as its serial numbers, name, and network identification. The results of this scan are processed by an identity sensor, which then passes the results to the identifier. The identifier then attempts to find a matching device in the CMDB. If the identifier finds a matching CI, the identifier either updates that CI or does nothing. If the identifier cannot find a matching CI, it either creates a new CI or does nothing. If Discovery is configured to continue, the identifier launches the exploration probes configured in the classification record to gather additional information about the device. Exploration probes can be multiprobes or simple probes.
    Important:
    Serial numbers are necessary for accurate asset tracking. If you modified baseline probes, sensors, or patterns, verify that they still discover serial numbers. In addition, do not configure sensors or patterns to modify the serial number syntax, such as adding a custom prefix. Non-standard serial numbers can lead to inaccurate asset tracking.

    CMDB identifier tables

    Table Description
    Identifier [cmdb_identifier] Stores all identifier rules.
    Identifier Entry [cmdb_identifier_entry] Stores all the identifier attributes.

    Identifier rules

    The default Discovery system contains these identifier rules, each of which is associated with a specific CI type (the sys_class_name field on the CI record) or the table in the Applies to field and contains the appropriate attributes for discovering CIs from the specified table. Where necessary to discover all possible occurrences of an attribute, tables from related lists (Search on tables) are included in the rule. For more information, see Create or edit a CI identification rule.

    Table 1. CMDB identifier rules
    Rule Applies to table/attributes Search on table/attributes
    ESX Server Rule ESX Server [cmdb_ci_esx_server]: correlation_id none
    Hardware Rule Hardware [cmdb_ci_hardware]
    • serial_number
    • serial_number_type
    • name
    • ip_address
    • mac_address
    • Serial Number [cmdb_serial_number]
      • serial_number
      • serial_number_type
    • Network Adapter [cmdb_ci_network_adapter]
      • ip_address
      • mac_address
    Storage Server Rule Storage Server [cmdb_ci_storage_server]
    • cim_object_path
    • name
    • serial_number
    • serial_number_type
    • mac_address
    • ip_address
    • Serial Number [cmdb_serial_number]
      • serial_number
      • serial_number_type
    • Network Adapter [cmdb_ci_network_adapter]
      • ip_address
      • mac_address
    WBEM Service Rule WBEM Service [cmdb_ci_wbem_service]: cim_object_path none

    Matching strategy for the hardware rule

    The sys_class_name cannot be an attribute for independent rules, such as cmdb_ci_hardware. If your Discovery identification strategy depends on matching a CI with a specific class, you must create a rule for each class you want to use for matching and specify that class in the Applies to field of the Identifier form.

    For example, you can create an identifier for a Linux server with different attributes than the Hardware Rule. You might want to use the machine name, IP address, and MAC address for identification. This is a solution for networks that use NIC bonding or teaming to increase available bandwidth. Bonded interfaces appear to be the same physical device and share the same IP and MAC addresses. The use of the name attribute allows Discovery to differentiate between the individual interfaces in the bonded channel.
    Important:
    If you create an identifier with the name attribute, avoid changing adapter names. Discovery will be unable to resolve existing CIs for renamed adapters. Discovery labels the Install Status of that CI as "Absent" and creates another CI.
    Your new rule would look like this:
    Figure 1. Linux identifier rule
    Linux identifier rule

    Evaluation order for Discovery identifiers

    Custom identifiers must have different Order values than those of the default identifiers. Discovery parses identifiers and attributes in sequence from low order numbers to high. You can create identifiers to run before or after the default identifiers, or mixed in with the identifiers from the base system. To avoid any identifier or rule from running, disable it by clearing the Active check box. The evaluation order for CMDB identifiers is established within each rule and only controls the parsing order of the attributes in that rule.

    Figure 2. Evaluation order in CMDB identifier rules
    CMDB identifier rules

    Properties for processing duplicate CIs

    You can control how Discovery handles duplicate CIs with properties installed with Identification and Reconciliation. Use the glide.identification_engine.skip_duplicates and glide.identification_engine.skip_duplicates.threshold properties. For more information, see Properties for Identification and Reconciliation.

    Properties that control identifier versions

    All instances use identifiers from the CMDB Identification and Reconciliation framework. Upgrades from pre-Geneva versions still preserve the legacy identifiers, but you can switch to the new identifiers using a property: glide.discovery.use_cmdb_identifiers. If you upgraded from a pre-Geneva version, you must manually add this property and set it to true to use the new identifiers. If you upgraded from Geneva or later releases, this property is available in the System Properties [sys_properties] table. To preserve functionality in custom legacy identifiers, convert them to the new CMDB identifier rules format before enabling this property. The system does not reconfigure your custom identifiers to the new framework automatically.
    Note:
    When Service Mapping is active, the new identifiers from the CMDB Identification and Reconciliation framework are always used regardless of the property value.