Recognize Shared Address Space Without Treating It as a Complete CGNAT Test

Manual WAN-address interpretation; no automatic collection of public IPs.

Applies to: Manual WAN-address interpretation; no automatic collection of public IPs.

Checked: 2026-11-01 · Risk: low · Status: source-grounded editorial draft; not hands-on tested.

Before you begin

Inspect the WAN address locally. RouterFix should classify it in the browser and avoid storing the literal address, screenshot or MAC.

Procedure

1. Check whether the address belongs to 100.64.0.0/10, the shared-address block defined by RFC 6598.
2. Distinguish that block from ordinary private LAN addressing and from a globally reachable endpoint.
3. Record whether a separate upstream router exists and ask the ISP about the actual address/port policy.
4. For an inbound VPN server, assess reachability separately from whether outbound web browsing works.

Verify the result

The result should say “shared address range detected” or “insufficient evidence,” not claim a full diagnosis from one number.

Undo or recover

This classification changes no device setting. Clear local input when finished.

Stop and escalate

Do not recommend random port opening when the upstream service does not permit inbound reachability.

Evidence and interpretation limits

The address range is an IETF fact; interpretation of a particular customer topology is a conditional diagnostic inference.

The steps above combine paraphrased official instructions with an original safety and test workflow. They are not a verbatim manual, a guaranteed fix, or evidence of a common hardware defect.

Official sources

• RFC 6598 shared address space for carrier networks — ietf-rfc6598; access: full_text.

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