Reserved IPs in Cloud: What Every Cloud Engineer Should Know


Reserved IP addresses are IPs within a subnet that cannot be assigned to virtual machines or other resources because the cloud provider keeps them for internal networking functions.

They exist to ensure the network works properly (routing, DNS, gateway, etc.).

In cloud platforms like :-

  • Microsoft Azure
  • Amazon Web Services
  • Google Cloud Platform

When you create a subnet, some IP addresses are automatically reserved by the provider.

Reserved IPs Inside a Subnet (Automatically Reserved by Cloud Provider)

Cloud Provider

Total Reserved IPs per Subnet

Reserved IP Addresses

Notes

Microsoft Azure

5

First 4 + Last 1

Same rule across all VNets

Amazon Web Services (AWS)

5

First 4 + Last 1

Same behavior as Azure

Google Cloud Platform (GCP)

4

First 2 + Last 2

Slightly different from Azure/AWS

 Example (Subnet: 10.0.0.0/24)

Provider

Reserved IPs in 10.0.0.0/24

Azure

10.0.0.0 – 10.0.0.3 and 10.0.0.255

AWS

10.0.0.0 – 10.0.0.3 and 10.0.0.255

GCP

10.0.0.0 – 10.0.0.1 and 10.0.0.254 – 10.0.0.255

 

 Why Azure/AWS reserve 5 IPs but GCP reserves 4?

  • DNS Architecture Difference

Azure and AWS traditionally reserve a dedicated internal DNS IP inside the subnet.
GCP handles DNS slightly differently at the VPC level, so it does not need to reserve an extra IP in every subnet.

  •  Internal Network Design Choices

Each cloud provider built its SDN (Software Defined Network) differently.
The number of reserved IPs is simply an architectural decision.

There’s no functional limitation — just implementation difference.

Why These IPs Are Reserved?

Generally reserved for:

  • Network address
  • Default gateway
  • DNS services
  • Future use by provider
  • Broadcast address (except Azure which doesn't use broadcast traditionally but still reserves last IP)

Important: Two Meanings of “Reserved IP”

In cloud environments, “reserved IP” can mean two different things:

  •  System-Reserved (Inside Subnet)

Automatically reserved by cloud provider (explained above).

  •  User-Reserved (Static Public IP)

When you reserve a public IP so it doesn’t change.

Examples:

  • Azure → Static Public IP
  • AWS → Elastic IP
  • GCP → Static External IP
Older