IP addresses in Azure fall into two categories: dynamic and reserved. By default, public IP addresses are dynamic. To prevent IP addresses from changing, you can reserve an IP address. Reserved IPs can be used only as a VIP, ensuring that the IP address for a service will be the same even as resources are shutdown or deallocated. Furthermore, you can convert existing dynamic IPs used as a VIP to a reserved IP address.
You can use reserved IP addresses for scenarios such as: