Set Up 1&1 IONOS DynDNS – Use Your Own Domain as Dynamic DNS

• What Is DynDNS?
• Requirements For IONOS DynDNS
• Step 1: Create An API Key In The IONOS Developer Portal
• Step 2: Activate The DynDNS Service For Your Domain
• Step 3: Update The A Record With Script And Cronjob
• Create Script ionos_update.sh
• Create Cronjob
• Example Setup With Router, Reverse Proxy And Wildcard Certificates
• Alternatives To 1&1 IONOS DynDNS
• Security: What You Should Keep In Mind
• FAQ About 1&1 IONOS DynDNS
• Glossary

Many internet connections use a dynamic public IP address that changes regularly. For browsing or streaming this is no problem, but as soon as you want to access devices in your home network or office from the internet it gets complicated.

The typical solution is Dynamic DNS: a hostname that always points to your current IP. Instead of using third party services, you can turn your own 1&1 IONOS domain into a DynDNS domain and keep full control over your DNS configuration.

Benefits of using 1&1 IONOS DynDNS with your own domain:

• full control over your domain and DNS records
• no dependency on free third party DynDNS providers
• clean setup for homelab, NAS, home office or small business networks

In this guide I will show you how to set up 1&1 IONOS DynDNS, how the script for updating the A record works, which alternatives exist and what you should keep in mind regarding security and configuration.

What Is DynDNS?

DynDNS stands for Dynamic DNS. A DynDNS service links a fixed domain name to a changing IP address. Whenever your internet provider assigns a new IP address, the DNS A record is updated automatically so your DynDNS hostname always points to the correct connection.

Typical use cases:

• remote access to NAS, homelab or servers
• Remote Desktop, RDP or SSH to your home network
• VPN access for you and your colleagues
• accessing self hosted services like Home Assistant, Nextcloud, Bitwarden, Jellyfin or Nginx Proxy Manager

Instead of remembering the current IP, you simply connect to the same DynDNS domain every time.

Requirements For IONOS DynDNS

To set up 1&1 IONOS DynDNS you need:

• a 1&1 IONOS account with at least one domain
• optionally the IONOS DNS Pro plan with DNSSEC and Anycast (recommended for more stability)
• a server or computer in your local network that can run a small update script on a schedule
  • for example a Linux server, Raspberry Pi, Proxmox LXC container or NAS
• a router that supports port forwarding
• basic knowledge of Linux shell and SSH

It is very convenient to use a dedicated subdomain as your DynDNS target, for example dyndns.your-domain.com. You can then point other domains and subdomains to it using CNAME records.

Step 1: Create An API Key In The IONOS Developer Portal

1. Log in to the IONOS Developer Portal: https://developer.hosting.ionos.de/keys
2. Click on “Erstellen Sie einen neuen Schlüssel” or “Create new key”
3. Enter a meaningful name, for example nginx, dyndns or homelab
4. You will now see two important values:
   • prefix
   • encryption or secret

Write down both values and store them in a safe place like a password manager. Later you will use them in the form prefix.secret as your IONOS DNS API key. After closing the page you cannot view the secret again.

Step 2: Activate The DynDNS Service For Your Domain

Next you activate the DynDNS service for your domain or subdomain and receive an update URL.

On a Linux system you can do this with a simple curl command:

#!/bin/bash

curl -sS -X POST "https://api.hosting.ionos.com/dns/v1/dyndns" \
  -H "Accept: application/json" \
  -H "Content-Type: application/json" \
  -H "X-API-Key: prefix.secret" \
  -d '{
    "domains": ["dyndns.your-domain.com"],
    "description": "My DynamicDns"
  }'

Adjust the following values:

• prefix.secret: your IONOS API key created in step 1
• dyndns.your-domain.com: the DynDNS domain or subdomain you want to use

As a response you will get a JSON object. The most important field is the updateUrl, for example:

{
  "bulkId": "1ba1e328-504a-46ca-ba6c-3262a468883e",
  "updateUrl": "https://ipv4.api.hosting.ionos.com/dns/v1/dyndns?q=YOUR_TOKEN",
  "domains": ["dyndns.your-domain.com"],
  "description": "My DynamicDns"
}

This updateUrl is your real IONOS DynDNS link. Every time the URL is called, the DNS A record of your DynDNS domain is updated to the IP address of the client that sends the request.

Step 3: Update The A Record With Script And Cronjob

To keep your 1&1 IONOS DynDNS domain up to date you need to call the updateUrl regularly and automatically.

Create Script ionos_update.sh

Create a folder in your home directory:

mkdir -p ~/ionos
nano ~/ionos/ionos_update.sh

Content of the file:

#!/bin/bash

# IONOS DynDNS update
curl -sS "https://ipv4.api.hosting.ionos.com/dns/v1/dyndns?q=YOUR_TOKEN"

Replace YOUR_TOKEN with the token from the updateUrl.

Make the script executable:

chmod +x ~/ionos/ionos_update.sh

Create Cronjob

Open the cron configuration:

crontab -e

Add the following line:

*/15 * * * * ~/ionos/ionos_update.sh >/dev/null 2>&1

The script now runs every 15 minutes and updates your IONOS DynDNS domain. For most home internet connections this interval is more than enough.

If you want faster updates, you can change */15 to */5 for every 5 minutes, but in practice 15 or 30 minutes are usually fine.

Example Setup With Router, Reverse Proxy And Wildcard Certificates

A common IONOS DynDNS homelab setup looks like this:

1. You create dyndns.your-domain.com in the IONOS DNS panel.
2. This subdomain is configured as your IONOS DynDNS domain and is updated via the ionos_update.sh script.
3. All other domains and subdomains such as home.your-domain.com or media.your-domain.com point via CNAME to dyndns.your-domain.com.
4. Your router (for example Lancom, FritzBox, UniFi, OpenWrt) forwards ports 80 and 443 to an internal Nginx server or to Nginx Proxy Manager.
5. In Nginx Proxy Manager you create one proxy host per service and request free Let us Encrypt certificates.
6. With the IONOS DNS challenge you can even create wildcard certificates for *.your-domain.com and terminate TLS directly on the reverse proxy.

The big advantage of this IONOS DynDNS setup: you only maintain one DynDNS subdomain, but you can host as many services and HTTPS domains behind it as you like.

Alternatives To 1&1 IONOS DynDNS

If you do not use IONOS or want to compare other dynamic DNS providers, the following overview might help:

Provider	Domain or hostname	Authentication	Price	Notes
1&1 IONOS DynDNS	your own domain, subdomains	API key and update URL	included in plan	full control, perfect if you already use IONOS DNS
DuckDNS	*.duckdns.org	token in URL	free	simple, popular, third party subdomain
No-IP Free	No-IP subdomain	account login	free or paid	free plan requires regular confirmation
dynv6	own domain or subdomain	token in URL	free	good IPv6 support, works well for self hosted services
Router built in DDNS	depends on router vendor	vendor specific	depends on service	easy setup, sometimes less flexible than custom DNS API

Some routers, for example many FritzBox models, can send DDNS updates directly. In that case you can often configure a custom DDNS provider and use your IONOS DynDNS update URL there. Then you do not need a Linux script at all.

Security: What You Should Keep In Mind

• Treat the prefix and secret of your API key like a password and never share them in screenshots or public repositories.
• The server that runs your IONOS DynDNS update script should be well secured and updated regularly. If this system is compromised, an attacker could change your DNS records.
• Only forward the ports in your router that are really necessary. For administrative access use a VPN like WireGuard or OpenVPN instead of exposing SSH or RDP directly.
• Protect web interfaces behind your reverse proxy with strong passwords, two factor authentication and rate limiting where possible.

A secure IONOS DynDNS setup is just as important as a working one.

FAQ About 1&1 IONOS DynDNS

Can I update multiple domains at once?
Yes. When you create the DynDNS configuration you can pass an array with several domains in the JSON body. All listed domains are then updated via the same IONOS DynDNS update URL.

Does IONOS DynDNS support IPv6?
Yes. You can optionally add parameters like ipv4= or ipv6= to the update URL. If you do not pass anything, IONOS usually uses the IP address of the client that sends the update request.

Can I configure IONOS DynDNS directly in my router?
Many routers offer a “custom DynDNS” or “user defined DynDNS” option. There you can enter the IONOS DynDNS update URL including token. The required format depends on the router, but in many cases username and password can be left empty because the token in the URL is enough.

How fast do DNS changes take effect?
That depends on the TTL (time to live) of your DNS records and on the caching behavior of your internet provider. In practice updates are usually active within a few seconds up to a couple of minutes.

Do I really need Linux for IONOS DynDNS?
No. You can also call the IONOS DynDNS update URL from Windows using a PowerShell script and the Windows Task Scheduler, or from a NAS that supports scheduled tasks or cronjobs. Linux is simply the most common option in homelabs.

Glossary

DynDNS / DDNS
Dynamic DNS – a service that automatically updates a domain name to the current IP address of your internet connection.

A record
DNS record that maps a hostname to an IPv4 address.

AAAA record
DNS record that maps a hostname to an IPv6 address.

CNAME record
Canonical name – a DNS record that makes one domain or subdomain an alias of another hostname. The CNAME itself does not store an IP address. Example: home.your-domain.com is a CNAME pointing to dyndns.your-domain.com. When the A record of dyndns.your-domain.com changes, the CNAME automatically follows without any additional changes.

API key
Secret key that you use to authenticate against an API. In the IONOS DNS API the key consists of a prefix and a secret combined as prefix.secret.

Update URL
Special URL provided by the IONOS DynDNS service. Each HTTP request to this URL updates the DNS records of your DynDNS domain.

TTL (Time To Live)
Defines how long DNS information may be cached by resolvers and clients before it has to be requested again.

Reverse proxy
Server that receives incoming HTTP or HTTPS requests from the internet and forwards them to internal services, for example Nginx or Nginx Proxy Manager.

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