Creating and Managing IP Prefixes in Netbox via the Web UI

Desired outcome

You want to define a new IP address block (prefix) in Netbox so that it can be used for allocating individual IP addresses, tracking utilization, and associating the block with a site, VRF, and optional role.

Prerequisites

• A running Netbox instance (v2.9 or later).
• A user account that has the Prefixes add permission (typically granted via the Prefixes object permission).
• Knowledge of the target site and VRF (or the global table if no VRF is used).
• The CIDR notation of the prefix you intend to create (e.g., 10.0.0.0/24 or 2001:db8:abcd::/48).
• Optional: a role (e.g., WAN, LAN) and any descriptive tags you want to apply.

Procedure

1. Navigate to the Prefixes list

   In the Netbox sidebar, choose IPAM → Prefixes. This displays all existing prefixes.

2. Start the creation form

   Click the Add Prefix button (green plus icon) at the top right of the list.

3. Enter the CIDR

   In the Prefix field, type the CIDR block (e.g., 10.10.20.0/24). Netbox will automatically validate the format.

4. Assign site and VRF

   Use the Site dropdown to select the physical or logical location where the prefix belongs. If your deployment uses VRFs, choose the appropriate VRF from the VRF dropdown; otherwise leave it set to Global (the default routing table).

5. Set status, role, and description

   Choose a Status (e.g., Active, Planned, Deprecated). For a newly allocated block, Active is typical. Optionally pick a Role to help with filtering and reporting. Add a Description that explains the purpose (e.g., Guest Wi‑Fi subnet for building B). You may also add Tags for custom categorization.

6. Save the prefix

   Click the Save button. Netbox will either create the prefix or return an error if the CIDR overlaps an existing prefix in the same VRF.

Verification checks

1. Confirm presence in the list

   After saving, you should be redirected to the prefix detail page. Verify that the Prefix, Site, VRF, Status, and any Role or Tags match what you entered.

2. Check address space utilization

   On the prefix detail page, the Utilization section shows how many addresses are free versus used. For a newly created prefix, the used count should be 0 (unless you have already assigned addresses manually).

3. Test address allocation

   Navigate to IPAM → Addresses → Add. In the Address field, type an IP from the newly created prefix (e.g., 10.10.20.5/24) and save. If the address is accepted without error, the prefix is correctly active and available for assignment.

Rollback options

If you discover that the prefix was created in error (wrong CIDR, site, or VRF), you can remove it:

1. Go to IPAM → Prefixes and locate the prefix (you can search by its CIDR).
2. Open the prefix detail page and click the Delete button (trash can icon).
3. Confirm the deletion in the dialog.
4. Note: Deleting a prefix does not automatically reclaim any IP addresses that were assigned from it. Those addresses will become “orphaned” and must be manually deleted or reassigned before the prefix can be removed without leaving dangling references.

Limitations and practical considerations

• Overlap prevention: Netbox will reject any new prefix that overlaps an existing prefix within the same VRF. Ensure you have checked the existing prefix list (or used the Check for overlaps feature in the UI) before attempting to create a new block.
• Status vs. reclamation: Changing a prefix’s status to Deprecated does not free its assigned IP addresses. You must manually delete or reassign those addresses first if you intend to reuse the space.
• Bulk import caveats: When using the CSV import (IPAM → Prefixes → Import), review the import log for any rows that failed due to overlap or missing site/VRF. Correct those rows and re‑import only the failed entries.
• Permissions: If you receive an authorization error when clicking Add Prefix, verify that your user role includes the prefixes.add permission. Contact your Netbox administrator if needed.

Summary

Creating an IP prefix in Netbox is a straightforward web‑UI task that requires proper CIDR input, site/VRF selection, and status assignment. After creation, verify the prefix appears correctly, shows zero utilization, and allows address allocation. If a mistake is made, delete the prefix after cleaning up any assigned addresses, and be mindful of overlap rules and status‑related reclamation limitations.