---
sourceDocument: Australia Telecommunications Network Inventory
sourceDocumentLink: https://servicenow-prod.fluidtopics.net/r/telecom-network-inventory

 Release :

    - australia

ft:locale :

    - en-US

ft:publication_title :

    - Australia Telecommunications Network Inventory

ft:clusterId :

    - telninv

bundleId :

    - telninv

workflow :

    - Customer and Industry


---

# CIDR validation rules for IP Address Blocks and IP Subnetworks

# CIDR validation rules for IP Address Blocks and IP Subnetworks {#ariaid-title1}

Release version: Australia  
Updated September 10, 2026  
![](https://www.servicenow.com/docs/portal-asset/ico-clock) 1 minute to read  
The CIDR value entered on an IP Address Block or IP Subnetwork record is validated when the record is saved. Invalid CIDR values are rejected with an inline error message; the record cannot be saved until the value passes all rules.
The same validation applies to both IPv4 and IPv6, with the protocol-specific differences noted in each rule.

## Format and value rules {#cidr-validation-rules__format-and-value-rules}

These rules apply to every CIDR value, whether on an IP Address Block or an IP Subnetwork.
{#cidr-validation-rules__format-value-rules-table__entry__4}

| Rule | What's checked | Rejected example | Error message |
|-|-|-|-|
| Valid CIDR format | The value is well-formed CIDR notation: an IP address, a slash, and a prefix length. | 192.168.1.0 (no prefix) | "Invalid CIDR format: Valid CIDR should contain exactly one slash" equivalent message for IPv6. |
| Valid prefix range | IPv4 prefix is 0--32. IPv6 prefix is 0--128. | 10.0.0.0/55 | "Invalid CIDR. Format prefix must be a number between 1 and 32 inclusive" |
| Valid IP address | The address portion is a syntactically valid IPv4 or IPv6 address. | 192.168.1.300/24 (octet \> 255) | "IP address is not valid" |
| Host bits zero | The address portion is the network address --- all host bits are zero relative to the prefix. | 172.16.5.10/24 (should be 172.16.5.0/24) | "Invalid CIDR format: Must be a valid IPv4/IPv6 network address matching the prefix" |
[ ]

{#cidr-validation-rules__format-value-rules-table}
**Related tasks**   

* [Create an IP Address Block record](https://servicenow-prod.fluidtopics.net/S7~AWj2an5aZ90dtgd~GTw "Create an IP Address Block record to define a top-level IP address range, expressed in Classless Inter-Domain Routing (CIDR) notation. The block becomes the parent for one or more IP Subnetworks. Supports both IPv4 and IPv6.")
* [Create an IP Subnetwork record](https://servicenow-prod.fluidtopics.net/9uvIJPRcTs8lUhUZ167X8A "Create an IP Subnetwork record to subdivide an IP Address Block or to nest a subnetwork within an existing IP Subnetwork. The subnetwork's CIDR must fall within its parent's range. This task supports both IPv4 and IPv6.")  
**Related reference**   

* [Hierarchy rules for IP Subnetworks](https://servicenow-prod.fluidtopics.net/w23g6E9ewprlk5TMK~fNmQ "These rules apply only when creating or updating an IP Subnetwork (which always has a parent — either an IP Address Block or another IP Subnetwork).")
* [IP Address Block form](https://servicenow-prod.fluidtopics.net/3_uKnkKuf6RtUa~Ubb6y2w "The IP Address Block form defines a top-level IP address range using CIDR notation. Use this reference to understand the available fields and their behavior.")
* [IP Subnetwork form](https://servicenow-prod.fluidtopics.net/FCJ5Na8kJ40qK1t_dzCQXQ "The IP Subnetwork form defines a subdivision of an IP Address Block or a nested subdivision of another IP Subnetwork.")