Just like a physical NGFW appliance, an Azure-hosted instance has the ability to support multiple IP addresses on a single, usually WAN, interface. Most of the configuration is done in Azure itself.
The article below from Microsoft outlines how to add the IP addresses in your Azure container.
Once that process is done, you then need to go into your NGFW to add the IP's as aliases on the WAN interface.
- In the Admin UI, go to Config > Network > Interfaces, then click Edit for the External interface.
- At the bottom of the IPv4 Configuration tab, Click the Add button directly under "IPv4 Aliases".
- Enter the address and netmask for the new IP.
- Repeat this process for every additional IP you wish to add.
- Click Done to close out of the "Edit Interface" window, then click Save to apply the new IP addresses.