IPAM

Your first VPC uses 10.0.0.0/16. You track it in a spreadsheet. Your second VPC uses 10.1.0.0/16. You add a row. By the time you have 20 VPCs across 4 AWS accounts and 3 regions, the spreadsheet has become a lie. Someone created a VPC with an overlapping range. Someone forgot to update the sheet. Now two VPCs can't be peered, and nobody knows which IPs are actually in use.

IPAM. IP Address Management, solves this by centralizing IP allocation, tracking usage, and enforcing non-overlapping ranges across your entire cloud infrastructure. AWS offers a managed service (VPC IPAM). Azure has similar capabilities. For multi-cloud, tools like NetBox, Infoblox, or phpIPAM serve the same purpose.

This isn't a tool you need on day one. But the moment you have multiple VPCs, multiple accounts, or need VPC peering. IP governance becomes non-negotiable. The cost of fixing overlapping ranges after the fact is orders of magnitude higher than planning them upfront.

An IPAM system manages a hierarchy of IP pools:

Top-level pool: Your organization's entire IP allocation (e.g., 10.0.0.0/8)

Regional pools: Carved from the top level (e.g., 10.0.0.0/12 for us-east-1, 10.16.0.0/12 for eu-west-1)

Account/VPC pools: Carved from regional pools (e.g., 10.0.0.0/16 for production-account VPC)

AWS VPC IPAM features:

• Automatically discovers existing VPC CIDRs across all accounts in your organization
• Enforces allocation rules, no VPC can use a CIDR that overlaps with another
• Monitors IP utilization, alerts when a pool is running low
• Integrates with AWS Organizations for multi-account governance