Why am I seeing the erorr 'Network Already Exists" or "Network is a subnet of an existing closed network" when adding a network identity for Cisco Umbrella DNS Layer Security?

Introduction

This document outlines what is required in the event you are trying to register a network but receive an error or Support has asked you to provide documentation to verify ownership of a network registration.

Symptoms

You may run across either of the following errors when attempting to add a network identity:

Network Already Exists.

Network is a subnet of an existing closed network.

These errors are a result of the network you are trying to add already being registered to another Cisco Umbrella customer. If you see these errors please contact Support.

Required Documentation

Depending on the IP address, Support may require proof of ownership of the network.

Acceptable forms of documentation are as follows:

• A letter from your ISP showing that you have been assigned the address. The IP Address reflected on this letter should match with the network you are trying to register. 
• An original email from your ISP's customer service department confirming that you have been assigned the address you are trying to register.
• A recent invoice from your ISP that shows you have been assigned the address. The IP address you are trying to register should be shown on the invoice. 

If you are unable to provide any of the above documentation Support may not be able to register the IP address under your organization.