Quick Discovery works, but Scheduled Discovery completely misses specific IP addresses within range

[FarsabH]

I am facing a strange issue with ITOM Discovery where specific devices are not being discovered during our automated schedules, but they discover perfectly via Quick Discovery.

The Setup:

• Subnet Block: x.x.x.x/20
• Example Target IP: x.x.x.x
• MID Server: Using the exact same MID server for both the schedule and the Quick Discovery test.

The Problem:

1. When I run a Scheduled Discovery containing the block x.x.x.x/20, it finishes running but completely misses the target IP (x.x.x.x). The device is not updated or created.
2. Even when I broke down the /20 block into smaller, sequential /24 IP Range Sets (like x.x.x.x/24) inside the schedule, the schedule still skipped the device.
3. However, if I use Quick Discovery from the target IP or add this exact single IP directly to the Quick Discovery range, the device is found instantly and creates/updates the CI in the CMDB perfectly.

[Vishnu-K]

Hi @FarsabH ,

When doing quick discovery you get to use all the credentials in the ServiceNow credentials table but if you have attached a credential alias to the schedules and by any chance the credential for that target device is not in that credential alias then it won't get discovered . Once after doing quick discovery check the Classification input playload and see which credential it used and then check if that credential is in the respective credential alias which is attached to the discovery schedule.

Hope this helps, if it helped you please do mark it as helpful and accept the solution.

Thanks,

Vishnu

[FarsabH]

Thanks for the suggestion!

I checked both the Discovery Schedule and the working Windows Credential, and neither of them has a Credential Alias attached. Both are configured globally, so the schedule isn't restricting credential selection.

Interestingly, when I tested adding a smaller sub-range  of 10 IPs directly to the schedule, the target IP  discovered perfectly but not on /24 block. 

[SGienow]

Take a look at the discovery log for the schedules that do not work.  There you can find everything that happened in the process, and why the device is not being updated/found/whichever.