30 June 2020

A simple Bash script and helper to accept incoming SSH traffic using port forwarding on a router, with a dynamic DNS through DigitalOcean.

Following: DigitalOcean DDNS Guide

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• Requirements
• Setup Instructions
  • Get a DigitalOcean API Token
  • Set Up a Project
  • Add DNS Record (A)
  • Get DNS Record ID
  • Update DNS
  • Set Up a Cron Job
  • Configure Port Forwarding
  • Connect via SSH
  • Install update-dns.sh to /usr/local/bin
  • Keep Local Machine Awake

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Requirements

• DigitalOcean account
• API token for DNS updates
• A local machine with SSH server enabled ("Remote Login")
• Router capable of port forwarding (example: Apple Airport Base Station)

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Setup Instructions

1. Get a DigitalOcean API Token

Create a Personal Access Token

2. Set Up a Project

Example: Use O-R-G as your project name.

3. Add DNS Record (A)

Point basement.o-r-g.net to your IP. This DNS record will be updated by a local Bash script.

4. Get ID of the DNS Record

Use the get-dns-id.sh script:

./get-dns-id.sh

5. Update DNS

Add the DNS record ID and API token to .zshrc as enviroment variables then run update-dns.sh:

nano /Users/me/.zshrc
./update-dns.sh

6. Set Up a Cron Job

Keep the DigitalOcean DNS record updated every 5 minutes:

crontab -e

Add the following line:

*/5 * * * * /usr/local/bin/update-do-ddns >> /Users/me/log.txt

7. Configure Port Forwarding on Router (Airport Base Station)

Following Apple Discussions: Port Mapping

Steps:

• Reserve a DHCP static IP for the local computer.
• Forward external port 22 to this static IP.

Requirements:

• MAC address (System Preferences → Network).
• Static local IP.

List all local IPs and MAC addresses:

arp -a

Example output:

xx:xx:xx:xx:xx:xx
10.0.1.x

Set up port forwarding:

• Choose "Remote Login - SSH" (public TCP, port 22 points to local static IP).
• Restart the Base Station.

7. Set static ip

Set static ip for local computer with MAC address specified in Step 7: System Settings : Network : Wifi : Details : TCP/IP : Configure IPv4 : Using DHCP with Manual Address

8. Connect via SSH

Ensure sshd is running locally ("Remote Login" enabled in Sharing).

Connect using:

ssh someone@somewhere.com

9. Install update-dns.sh to /usr/local/bin

cp update-do-ddns.sh /usr/local/bin/update-do-ddns

10. Set Local Computer to Stay Awake

Run on startup:

caffeinate -d

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✅ Your system should now accept incoming SSH traffic dynamically using DDNS and port forwarding.