AVM FRITZ!Box Cloudflare DNS-service

This project has some simple goals:

• Offer a slim service without any additional service requirements
• Allow for two different combined strategies: Polling (through FRITZ!Box SOAP-API) and Pushing (FRITZ!Box Custom-DynDns setting).
• Allow multiple domains to be updated with new A (IPv4) and AAAA (IPv6) records
• Push those IP changes directly to Cloudflare DNS
• Deploy in docker compose

If this fits for you, skim over the CNAME workaround if this is a better solution for you, otherwise feel free to visit the appropriate strategy section of this document and find out how to configure it correctly.

CNAME record workaround

Before you try this service evaluate a cheap workaround, as it does not require dedicated hardware to run 24/7:

Have dynamic IP updates by using a CNAME record to your myfritz address, found in Admin > Internet > MyFRITZ-Account. It should look like [hash].myfritz.net.

This basic example of a BIND DNS entry would make intranet.example.com auto update the current IP:

$TTL 60
$ORIGIN example.com.
intranet IN CNAME [hash].myfritz.net

Beware that this will expose your account hash to the outside world and depend on AVMs service availability.

Strategies

FRITZ!Box pushing

You can use this strategy if you have:

• access to the admin panel of the FRITZ!Box router.
• this services runs on a public interface towards the router.

In your .env file or your system environment variables you can be configured:

Variable name	Description
DYNDNS_SERVER_BIND	required, network interface to bind to, i.e. :8080.
DYNDNS_SERVER_USERNAME	optional, username for the DynDNS service.
DYNDNS_SERVER_PASSWORD	optional, password for the DynDNS service.
DYNDNS_SERVER_PASSWORD_FILE	optional, path to a file containing the password for the DynDNS service. It's recommended to use this over DYNDNS_SERVER_PASSWORD.

Now configure the FRITZ!Box router to push IP changes towards this service. Log into the admin panel and go to Internet > Shares > DynDNS tab and setup a Custom provider:

Property	Description / Value
Update-URL	http://[server-ip]/ip?v4=<ipaddr>&v6=<ip6addr>&prefix=<ip6lanprefix>
Domain	Enter at least one domain name so the router can probe if the update was successfully.
Username	Enter '_' if DYNDNS_SERVER_USERNAME is unset.
Password	Enter '_' if DYNDNS_SERVER_PASSWORD and DYNDNS_SERVER_PASSWORD_FILE are unset.

If you specified credentials you need to append them as additional GET parameters into the Update-URL like &username=<username>&password=<pass>.

FRITZ!Box polling

You can use this strategy if you have:

• no access to the admin panel of the FRITZ!Box router.
• for whatever reasons the router can not push towards this service, but we can poll from it.
• you do not trust pushing

In your .env file or your system environment variables you can be configured:

Variable name	Description
FRITZBOX_ENDPOINT_URL	optional, how can we reach the router, i.e. http://fritz.box:49000, the port should be 49000 anyway.
FRITZBOX_ENDPOINT_TIMEOUT	optional, a duration we give the router to respond, i.e. 10s.
FRITZBOX_ENDPOINT_INTERVAL	optional, a duration how often we want to poll the WAN IPs from the router, i.e. 120s.

You can try the endpoint URL in the browser to make sure you have the correct port, you should receive an 404 ERR_NOT_FOUND.

Because FRITZBOX_ENDPOINT_URL is set by default on the docker image, you have to explicitly set it to an empty string to disable polling

Cloudflare setup

To get your API Token do the following: Login to the cloudflare dashboard, go to My Profile > API Tokens > Create Token > Edit zone DNS, give to token some good name (e.g. "DDNS"), add all zones that the DDNS should be used for, click Continue to summary and Create token. Be sure to copy the token and add it to the config, you won't be able to see it again.

In your .env file or your system environment variables you can be configured:

Variable name	Description
CLOUDFLARE_API_TOKEN	required if CLOUDFLARE_API_TOKEN_FILE is unset, your Cloudflare API Token.
CLOUDFLARE_API_TOKEN_FILE	required if CLOUDFLARE_API_TOKEN is unset, path to a file containing your Cloudflare API Token. It's recommended to use this over CLOUDFLARE_API_TOKEN.
CLOUDFLARE_ZONES_IPV4	comma-separated list of domains to update with new IPv4 addresses.
CLOUDFLARE_ZONES_IPV6	comma-separated list of domains to update with new IPv6 addresses.
CLOUDFLARE_API_EMAIL	deprecated, your Cloudflare account email.
CLOUDFLARE_API_KEY	deprecated, your Cloudflare Global API key.
CLOUDFLARE_API_KEY_FILE	deprecated, path to a file containing your Cloudflare Global API key. It's recommended to use this over CLOUDFLARE_API_KEY.

This service allows to update multiple records, an advanced example would be:

CLOUDFLARE_ZONES_IPV4=ipv4.example.com,ip.example.com,server-01.dev.local
CLOUDFLARE_ZONES_IPV6=ipv6.example.com,ip.example.com,server-01.dev.local

Considering the example call http://192.168.0.2:8080/ip?v4=127.0.0.1&v6=::1 every IPv4 listed zone would be updated to 127.0.0.1 and every IPv6 listed one to ::1.

Register IPv6 for another device (port-forwarding)

IPv6 port-forwarding works differently and so if you want to use it you have to add the following configuration.

Warning: FRITZBOX_ENDPOINT_URL has to be set for this to work.

To access a device via IPv6 you need to add it's global IPv6 address to cloudflare, for this to be calculated you need to find out the local part of it's IP. You can find out the local part of a device's IP, by going to the device's settings and looking at the IPv6 Interface-ID. It should look something like this: ::1234:5678:90ab:cdef. Sometimes the FritzBox seems to use a subnet, so you might need to add change it from something like ::1234:5678:90ab:cdef to ::1:1234:5678:90ab:cdef

Variable name	Description
DEVICE_LOCAL_ADDRESS_IPV6	required, enter the local part of the device IP

Docker compose setup

Here is an example docker-compose.yml with all features activated:

version: '3.7'

services:
  updater:
    image: ghcr.io/cromefire/fritzbox-cloudflare-dyndns:1
    network_mode: host
    # build:
    #   context: .
    environment:
      - FRITZBOX_ENDPOINT_URL=http://fritz.box:49000
      - FRITZBOX_ENDPOINT_TIMEOUT=30s
      - FRITZBOX_ENDPOINT_INTERVAL=3s
      - CLOUDFLARE_API_EMAIL=max@example.com
      - CLOUDFLARE_API_KEY=demo
      - CLOUDFLARE_ZONES_IPV4=test.example.com
      - CLOUDFLARE_ZONES_IPV6=test.example.com

Now we could configure the FRITZ!Box to http://[docker-host-ip]:49000/ip?v4=<ipaddr>&v6=<ip6addr>&prefix=<ip6lanprefix> and it should trigger the update process.

Docker build

A pre-built docker image is also available on this GitHub repository as ghcr.io/cromefire/fritzbox-cloudflare-dyndns:<version>. The version is something like 1.2 (you can leave out the patch version), please don't use latest directly, as it may break at any point with a major release.

You can use it with compose like this:

name: "dyndns"
services:
  updater:
    image: "ghcr.io/cromefire/fritzbox-cloudflare-dyndns:<version>"
    env_file: ./updater.env
    restart: unless-stopped
    ports:
      - "8080/tcp"

With your secret configure in the updater.env file next to it (as SOME_VARIABLE=<valua>).

The more raw approach would be to build and run it yourself:

docker build -t fritzbox-cloudflare-dyndns .
docker run --rm -it -p 8888:8080 fritzbox-cloudflare-dyndns

If you leave CLOUDFLARE_* unconfigured, pushing to Cloudflare will be disabled for testing purposes, so try to trigger it by calling http://127.0.0.1:8888/ip?v4=127.0.0.1&v6=::1 and review the logs.

Passing secrets

As shown above, secrets can be passed via environment variables. If passing secrets via environment variables does not work for your use case, it's also possible to pass them via the filesystem. In order to pass a secret via a file, append _FILE to the respective environment variable name and configure it to point to the file containing the secret. For example in order to pass the Cloudflare API token via a file, configure an environment variable with name CLOUDFLARE_API_TOKEN_FILE with the absolute path to a file containing the secret.

Here is an example docker-compose.yml passing the file cloudflare_api_key.txt from the host to the docker container using docker compose secrets:

name: "dyndns"
services:
  updater:
    image: ghcr.io/cromefire/fritzbox-cloudflare-dyndns:1
    network_mode: host
    environment:
      - DYNDNS_SERVER_BIND=:8080
      - CLOUDFLARE_API_TOKEN_FILE=/run/secrets/cloudflare_api_token
      - DYNDNS_SERVER_PASSWORD_FILE=/run/secrets/fb_server_password
      - CLOUDFLARE_ZONES_IPV4=test.example.com
      - CLOUDFLARE_ZONES_IPV6=test.example.com
    secrets:
      - cloudflare_api_token
      - fb_server_password

secrets:
  cloudflare_api_token:
    file: ./cloudflare_api_token.txt
  fb_server_password:
    file: ./fb_server_password.txt

See https://docs.docker.com/compose/how-tos/use-secrets/ for more information about docker compose secrets.

Metrics and Health Check

If you want to check whether the service is running correctly, you can configure these with the following variables:

Variable name	Description
METRICS_BIND	required, network interface to bind to, i.e. :9876
METRICS_TOKEN	token that has to be passed to the endpoints to authenticate
METRICS_TOKEN_FILE	path ot a file containing a token that has to be passed to the endpoints to authenticate. It's recommended to use this over METRICS_TOKEN.

The endpoint for prometheus-compatible metrics is /metrics, the endpoint for the health check is /healthz and the endpoint for liveness is /liveness on the configured network bind. If you chose to use a token, you'll have to append it using the query like /metrics?token=123456.

The difference between the liveness and the health endpoint is that the health endpoint will return 503 if any subsystem has an issue and 200 if not, while the liveness endpoint will always return 204 as long as the HTTP server is able to respond.

History & Credit

Most of the credit goes to @adrianrudnik, who wrote and maintained the software for years. After he moved on I stepped in at a later point when the repository was transferred to me to continue its basic maintenance should it be required.