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 Someone documented the CIDRs in a spreadsheet that's already out of date.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.
