Inability to Port Forward on 5G Hub with eero - Suspected CG-NAT

[NixB]

Hi Three Community,

I'm currently using the Three 5G Hub with the included eero router and am trying to set up port forwarding for a specific application on my MacBook Air (running macOS). I'm facing an issue where external connections are unable to reach my device, despite what appears to be correct configuration on my end.

Here's a summary of my setup and troubleshooting steps:

My Goal: To open port 8333 (TCP) on my public IP address and forward it to my MacBook Air's local IP address (192.168.4.26).

My Setup: ISP: Three UK 5G Home Broadband. Router: Three 5G Hub with integrated eero. Device: MacBook Air (running macOS). Public IP Address (as seen from external services): 188.28.168.58

Troubleshooting Steps Taken (and confirmed):

1. Local Server Verified: I have a simple Python HTTP server running on my MacBook, listening on port 8333. I confirmed using 'sudo lsof -i :8333' that the server is actively listening for incoming connections on *:8333. (Output: Python ... TCP *:8333 (LISTEN)). So, the application on my Mac is ready.

2. macOS Firewall Verified: I have confirmed that the macOS Firewall on my MacBook is completely disabled, meaning it is not blocking any incoming connections to my computer.

3. eero Port Forwarding Configuration Verified: I have an IP reservation set up in the eero app, ensuring my MacBook Air (As-MacBook-Air) consistently receives the local IP address 192.168.4.26. I have created a port forwarding rule in the eero app (named "nixB") for port 8333 (TCP), forwarding it to 192.168.4.26. This rule is confirmed as "Enabled."

The Problem:

Despite all these configurations, when I attempt to connect to 'http://188.28.168.58:8333' from an external network (specifically, from an SDF Public Access UNIX System using 'lynx' or 'w3m'), the connection fails with "Unable to connect to remote host." This indicates the connection is not even reaching my eero router.

My Suspected Cause:

Based on these symptoms, I strongly suspect that Three's 5G Home Broadband service utilizes Carrier-Grade NAT (CG-NAT). If my public IP (188.28.168.58) is being shared across multiple customers at Three's network level, then direct inbound port forwarding from the internet will not work, as my router isn't directly exposed with that public IP.

My Questions for Three Support / Community:

1. Can you confirm whether Three's 5G Home Broadband service (specifically with the 5G Hub and eero) uses Carrier-Grade NAT (CG-NAT) for IPv4 connections?

2. If it does, is there any option available (e.g., a different APN setting, a specific add-on, or a different service tier) to obtain a truly public, routable IPv4 address that would allow me to set up inbound port forwarding?

3. If a public IPv4 address isn't available, does Three's 5G service fully support globally routable IPv6 addresses? If so, could you provide guidance on how to ensure my devices receive a public IPv6 address that can be directly accessed for services like port forwarding?

Any insight or assistance the community or Three support can provide would be greatly appreciated. I'm keen to get this port forwarding working.

Thank you in advance for your help!

[MymsMan]

Other user have reported issues with port forwarding and I wasn't able to either

Instead I access my home network via VPN,  I use NordVPN's meshnet feature which allows me to connect to a home computer running NordVPN from my mobile phones and laptop and access all of the devices on my home network without having to open any ports or know what my external IP address currently is.

I used Nord because I already had a cheap subscription but it should work with other VPN systems

[PeteG]

Hello, NixB. 

The issue you are having would normally be caused by CGNAT, however CGNAT isn't used on the 3internet APN and should allow you to port forward normally. The 3internet is usually the default APN that's used on Home Broadband connections, but you can always double check the settings to make sure that's active just in case. 

Pete.