The short answer
Horizontal Discovery finds individual CIs; on its own it does not keep service maps current. Service Mapping ships two default schedules, All Applications and Load Balancer Services, that trigger top-down discovery across business services. ServiceNow's guidance is that both must run — horizontal discovery for the CIs, the Service Mapping schedules for the maps.
A common ITOM complaint: Discovery runs every night, the CI counts look healthy, and the service maps the business relies on are still out of date. The explanation is that two different kinds of discovery are involved, and often only one of them is being watched.
Two kinds of discovery
Horizontal discovery is the familiar kind: run against IP ranges, it discovers and updates individual CIs [1]. Service maps depend on something else. The Service Mapping plugin ships two schedules that are active by default — All Applications and Load Balancer Services — and they trigger the ServiceDiscoveryProbe, which runs a top-down discovery on the endpoints across all business services [1].
Why both have to run
ServiceNow's guidance is explicit: those two Service Mapping schedules need to run even when horizontal discovery is already discovering CIs by IP, because they are what keep the service maps updated [1]. Horizontal discovery keeps the parts current; the Service Mapping schedules keep current the picture of how those parts form a service.
Where to look first
- Whether the Service Mapping schedules are active and completing, not only whether horizontal Discovery ran.
- Which source populated the CIs in a stale map — Discovery, an import or an integration — before re-running anything.
- Relationship health on its own terms, rather than inferring it from a completeness percentage.
The wider point
ITOM tooling separates finding things from understanding how they fit together, and its schedules reflect that split. Many stale service maps are not a Discovery failure at all. They are a scheduling assumption nobody revisited.
Sources
- [1] ServiceNow, Service Mapping default schedules and Horizontal Discovery schedules — do we need both to keep service maps up to date? (KB0716614). Published 7 April 2024.Primary source
- [2] ServiceNow, CMDB Health KPIs — what they mean, how scores are calculated, and why CIs appear (or don't) on the CMDB Health dashboard (KB2607946). Published 6 November 2025.Primary source
Related questions
Does ServiceNow Discovery keep service maps up to date?
Not on its own. Horizontal Discovery discovers individual CIs. Service maps are kept current by Service Mapping's default schedules, All Applications and Load Balancer Services, which trigger top-down discovery across business services. ServiceNow's guidance is that both need to run.
What is the difference between horizontal discovery and Service Mapping?
Horizontal discovery discovers and updates individual CIs, typically across IP ranges. Service Mapping runs top-down discovery on the endpoints of business services to keep the service maps that connect those CIs up to date.