Question

A company is designing IP addressing for a new AWS environment that will host 40 VPCs across three Regions, all connected to an on-premises data center via Direct Connect and Transit Gateway. The on-premises network already uses 10.0.0.0/8 extensively with fragmented allocations. The network team wants to advertise the fewest possible summarized routes over the Direct Connect private VIF to on-premises while guaranteeing no overlap with existing on-premises space, and wants room to add more VPCs later. Which IP addressing strategy best meets these requirements?

Accepted Answer

Assign the AWS environment a single large aggregate from an unused private range (for example 172.16.0.0/12), sub-allocate a contiguous per-Region block, and carve VPC CIDRs from each Region block so routes can be summarized per Region.

Answer

Allocate each VPC a /16 from within the existing 10.0.0.0/8 on-premises range and rely on longest-prefix match to avoid conflicts.

Answer

Give every VPC a randomly chosen /24 from 192.168.0.0/16 to keep VPCs small, and advertise each /24 individually over the private VIF.

Answer

Use the same 10.10.0.0/16 CIDR for VPCs in all three Regions and rely on Transit Gateway route tables to keep traffic isolated.