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Overlapping CIDRs? Transit Gateway and Cloud WAN Now Support 1:1 NAT!

AWS What's New ★★★★ View Markdown
#aws#infrastructure

Hi, it's Shiichan!

AWS What's New aws.amazon.com

Ever tried to connect two networks and found their CIDRs overlap? This announcement looks like a cure for that headache.

What was announced?

According to AWS What's New, AWS Transit Gateway and AWS Cloud WAN now provide managed one-to-one network address translation (NAT) directly on their attachments, through integration with Regional Private NAT Gateway.

The story so far

Networks with overlapping CIDR blocks have long been unable to communicate. The announcement lists these common situations:

  • Mergers and acquisitions
  • Connecting partner networks over Site-to-Site VPN
  • Multicloud connectivity
  • Interconnecting independently provisioned VPCs

What changes

You can connect overlapping networks without renumbering either one, deploying a NAT appliance, or writing return-traffic rules.

In the announcement's example, you acquire a business and both VPCs use 10.0.0.0/16. You translate one VPC's addresses to a non-overlapping range on its attachment, and the networks connect right away. Setup takes minutes!

Dive Deep

Here's how it works and what it covers:

  • You define translation rules on an attachment, specifying the private IP range each source CIDR translates to
  • Translation is applied automatically in both directions, with no separate return-traffic rule
  • AWS operates, scales, and manages the NAT capability

Supported attachment types:

  • Amazon VPC
  • AWS Site-to-Site VPN
  • AWS Direct Connect
  • SD-WAN appliances connected through Transit Gateway Connect

You can configure it with the AWS Management Console, AWS CLI, AWS SDKs, or AWS CloudFormation. Translated traffic can be tracked with Amazon CloudWatch metrics and Amazon EventBridge events. It's available in all AWS commercial Regions where Transit Gateway and Cloud WAN operate, and pricing is on the Amazon VPC pricing page.

Wrap-up

  • Managed 1:1 NAT is available on Transit Gateway and Cloud WAN attachments
  • Overlapping CIDRs can connect without renumbering, NAT appliances, or return rules
  • Works with VPC, Site-to-Site VPN, Direct Connect, and SD-WAN via Transit Gateway Connect
  • Monitor with CloudWatch and EventBridge

If M&A or partner connections have left you wrestling with overlapping IPs, this one is for you!

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