Accessing an Intranet Machine from Anywhere Using FRP

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Background

Scenario:
You have an intranet machine (e.g., a computer in your company) without a public IP, and you want to access it from home or anywhere with internet connectivity. You might also want to host a website on this local machine.

Requirement:
You need access to a server with a public IP.

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Solution Overview

To achieve this, tools like FRP, ngrok, NPS, and Zerotier can be used. Here, we focus on FRP (Fast Reverse Proxy), an open-source tool. You can download the appropriate version for your operating system from the FRP GitHub Releases.

This guide demonstrates how to set up FRP for SSH access. For more features, refer to the FRP documentation.

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SSH Usage

File Setup

1. Place frps and frps.ini on the public server.
2. Place frpc and frpc.ini on the intranet machine.

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Accessing the Intranet Machine via SSH

Step 1: Configure the Public Server

Edit the frps.ini file:

# frps.ini
[common]
bind_port = 7000

Start frps in the background:

nohup ./frps -c ./frps.ini > /dev/null 2>&1 &

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Step 2: Configure the Intranet Machine

Edit the frpc.ini file. Replace x.x.x.x with the public server’s IP address:

# frpc.ini
[common]
server_addr = x.x.x.x
server_port = 7000

[ssh]
type = tcp
local_ip = 127.0.0.1
local_port = 22
remote_port = 6000

Start frpc:

./frpc -c ./frpc.ini

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Step 3: Connect to the Intranet Machine

From any external machine, connect via SSH. Replace x.x.x.x with the public server’s IP, and assume the username is test:

ssh -oPort=6000 test@x.x.x.x

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Important Notes

1. Ensure the ports used in FRP (e.g., 7000, 6000) are open on the public server’s firewall.
2. Each client machine needs a unique remote_port for mapping.

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Extending Access for Web Applications

To access tools like Jupyter Notebook or TensorBoard, simply add additional port mappings in frpc.ini. For example:

[jupyter]
type = tcp
local_ip = 127.0.0.1
local_port = 8888
remote_port = 8889

Then, access the application at https://x.x.x.x:8889.

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Using SSH on a Mobile Phone

For iOS, you can use Termius, which offers basic SSH functionality for free.

Steps to Set Up SSH in Termius

1. Open Termius.
2. Navigate to Hosts → Add New → Enter the remote IP, SSH username, and password, then save.
3. Connect to the host.

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Using SSH Keys in Termius

1. Open Termius.
2. Go to Keychain → Add Key (or use an existing key).
3. Copy the public key.
4. Append the Termius public key to the server’s ~/.ssh/authorized_keys file.
5. In Termius, edit the host, attach the created key, and save.
6. Connect to the server.

Enjoy secure and efficient SSH access from your mobile device!

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This guide enables you to set up remote SSH access to an intranet machine using FRP and explains how to extend its functionality for web applications and mobile devices.