Most teams manage their VPC IP ranges in a spreadsheet — until two VPCs overlap, a peering connection refuses to come up, and nobody can remember who owns which CIDR. Amazon VPC IP Address Manager (IPAM) is the feature that quietly solves all of this. It's one of the most underrated tools in AWS networking, and here's why.
The problem nobody talks about until it breaks
IP address planning feels trivial on day one. You spin up a VPC, pick 10.0.0.0/16, and move on.
Fast-forward a year. You now have a dozen VPCs across multiple accounts and two regions. Someone documented the CIDRs in a spreadsheet that's already out of date. Then you try to set up a VPC peering connection or attach a VPC to a Transit Gateway and you hit a wall:
Two VPCs were both created with
10.0.0.0/16. Overlapping CIDR ranges can't be peered or routed together. Now you're looking at re-IPing an entire VPC — a painful, high-risk migration — just because nobody had a single source of truth.
This is the silent tax of growing on AWS: IP sprawl. And it's exactly what IPAM was built to eliminate.
What is AWS VPC IPAM?
IPAM is a managed feature of Amazon VPC that gives you one place to plan, track, and monitor every IP address in your AWS environment. Instead of a spreadsheet, you get a live, automated system of record.
It's built around a few simple concepts:
- IPAM — the top-level resource that manages everything.
- Scopes — a container for pools. You get a private scope (internal RFC 1918 ranges) and a public scope, kept separate so ranges never collide.
- Pools — collections of CIDR ranges. Pools are hierarchical: a top-level pool can be carved into regional pools, then per-account or per-environment pools.
- Allocations — a CIDR handed out from a pool to a resource like a VPC.
Think of it like a filing cabinet: one big drawer (top pool), folders by region, sub-folders by account or environment.
Why it's so underrated: 5 things IPAM does for you
1. Automatic CIDR assignment (no more guessing)
Instead of a human picking a CIDR and hoping it's free, you tell IPAM "give this VPC a /24 from the dev pool" and it allocates a non-overlapping range automatically.
2. Overlap prevention across accounts and regions
Because every allocation comes from a managed pool, IPAM guarantees you can't hand out the same range twice. This is the killer feature for anyone running AWS Organizations with many accounts. No more peering failures or emergency re-IP migrations.
3. Real utilization monitoring
IPAM continuously tracks how much of each pool is in use and can alert you (via CloudWatch) before a pool runs out.
4. Public IPv4 cost control
Since AWS started charging for every public IPv4 address (about $0.005/hour each, attached or idle), unused Elastic IPs are real money leaking out monthly. IPAM's public IP insights show every public IPv4, what it's attached to, and whether it's idle — so you can release the ones you don't need.
5. Audit history and compliance
IPAM keeps a historical record of how your IP space has been allocated over time. When someone asks "what was using this CIDR three months ago?", you have an actual answer.
Free Tier vs Advanced Tier
- Free Tier — basic planning, tracking, and monitoring within a single account and region. Great for getting started.
- Advanced Tier — cross-account via AWS Organizations, cross-region pools, automated allocation, public IP insights, compliance monitoring, and usage history. Billed per active managed IP at a small hourly rate.
For any real multi-account org, the Advanced Tier almost always pays for itself by preventing even one re-IP migration.
How to get started (quick version)
- Create an IPAM in your operating region.
- In the private scope, create a top-level pool with your overall range (e.g.
10.0.0.0/8). - Carve out regional and environment pools beneath it.
- When creating new VPCs, choose "allocate CIDR from IPAM pool" instead of typing one in.
- Turn on public IP insights and hunt down idle public IPv4 addresses.
Pro tip: Even if you never automate VPC creation, just pointing IPAM at your existing environment to discover what you already have — and where it overlaps — is worth the setup time.
Takeaway
IPAM isn't flashy. But it solves a problem that gets exponentially more expensive the longer you ignore it — and most teams only discover it after a painful overlap has already broken something.
If you're running more than a couple of VPCs, set up IPAM before you need it. Treat your IP space like the shared, finite resource it actually is.
Originally published on srinun.in. I write about DevOps, AWS, and Kubernetes — connect with me on LinkedIn.
