Tagged: ddns

Setup DDNS/DynDNS in OpenWrt

I serving my small homepage stokito.com directly from my router with OpenWrt Linux — thus I don’t have to pay for any hosting because the router is anyway always online. My provider gives to my router some public IP which is changes sometimes: maybe about once per week. That is fine for me but I have to change it manually. Of course I can buy a static public IP from my internet provider but my goal is to have cheapest as possible website. So I need to automatically and periodically update the DNS A record with my current IP.

To solve this problem people uses Dynamic DNS (DDNS) which is de facto some pseudo protocol when router itself constantly registers it’s current IP on the DNS server. Most routers already have support of some DDNS providers where most popular are DynDNS.com and NO-IP.com or even manufactures like ASUS may have their own DDNS. Gamers and owners of IP cameras very often using this.

Unfortunately my DNS registrar doesn’t support DDNS protocol so I have to use some another. A good news is that OpenWrt already have a package ddns-scripts witch supports a lot of servers. I checked almost all DDNS providers that are supported my and choose DuckDNS.org.

DynDNS.com looks like one of the first DDNS providers and some other even tries to implement it’s API. But it’s paid and that’s not acceptable for me to because with the same money I just can buy a static IP. The NO-IP.com have some strange API problems with refreshing IP so there is even a separate script for OpenWrt ddns-scripts_no-ip_com. In the same time DuckDNS looks like was made by programmers for programmers. It allows to quickly register with Google account then they give you a generated random token instead of password and they have a good documentation.

So the API is so simple that I even was wondered why it was created the ddns-scripts package. In fact, all what you need to do is to register on DuckDNS and receive your token (i.e. password) then login to your OpenWrt LUCI admin panel, then open System / Scheduled Tasks and add the following line:

* */4 * * * wget -4 -q -O /dev/null http://www.duckdns.org/update/{YOURDOMAIN}/{YOURTOKEN}

i.e. each 4 hours you will send a HTTP get request to DuckDNS.

Then you can check logs of cron task in syslogs: System / System Logs. For example for my domain stokito.duckdns.org:

Mon Apr 22 18:52:00 2019 cron.info crond[12903]: USER root pid 14005 cmd wget -4 -q -O /dev/null http://www.duckdns.org/update/stokito/6c5se9d3-5220-440-b46-6873f9a

But for some reason this setup via Luci doesn’t worked for me so better to do the same with command line. Login and edit crontab:

ssh root@
root@OpenWrt:~# echo "42 */4 * * * /etc/update_ddns.sh" >> /etc/crontabs/root

or you can edit:

root@OpenWrt:~# crontab -e

The crontab -e opens vi editor for /etc/crontabs/root. Also note that I enabled the cron service just to be sure. See OpenWrt cron documentation for details.

Now put there a line like this:

42 */4 * * * /etc/update_ddns.sh

Note here that I added some random minute 42 to keep DuckDNS from requests waves if all users tries to update their DNS once in a hour. So please take some another minute too.

Then add this script:

wget -4 -q -O /dev/null http://www.duckdns.org/update/{YOURDOMAIN}/{YOURTOKEN}

to /etc/update_ddns.sh and chmod +x it.

Now you need to enable and restart cron service:

root@OpenWrt:~# /etc/init.d/cron enable
root@OpenWrt:~# /etc/init.d/cron restart
root@OpenWrt:~# logread | grep cron

The last command is useful to see cron logs. You may want to increase cronloglevel in /etc/config/system. If everything worked then in duckdns dashboard you’ll IP will be updated. See "Last time changed" field.

Then your router will be accessible with the new domain. For example for my domain

$ dig stokito.duckdns.org

; DiG stokito.duckdns.org
;; global options: +cmd
;; Got answer:
;; HEADER   HEADER- opcode: QUERY, status: NOERROR, id: 41868
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

; EDNS: version: 0, flags:; udp: 4096
;baba.stokito.com.		IN	A

stokito.duckdns.org.	60	IN	A

;; Query time: 212 msec
;; WHEN: Mon Apr 22 23:55:45 EEST 2019
;; MSG SIZE  rcvd: 129

Here you can see that DNS server (BTW that’s AdGuard) responded that IP of the domain stokito.duckdns.org. is i.e. my public IP.

Use regular domain as alias for DDNS

I already have a domain stokito.com and I would like to use it instead of the DDNS stokito.duckdns.org. DNS supports this and what I need to do is to add to my domain stokito.com a new record CNAME with the DDNS stokito.duckdns.org. But DNS spec allows this only for subdomains. I.e. I can map blog.stokito.com to the stokito.duckdns.org but I can’t do that for for root domain stokito.com. Not sure why but most domain registrants follow the rule. I added a subdomain record router.stokito.com and mapped via CNAME to stokito.duckdns.org and here is how it resolved now:

$ dig router.stokito.com
; DiG 9.11.5-P1-1ubuntu2.3-Ubuntu router.stokito.com
;; global options: +cmd
;; Got answer:
;; HEADER opcode: QUERY, status: NOERROR, id: 19506
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

; EDNS: version: 0, flags:; udp: 4096
;router.stokito.com.		IN	A

router.stokito.com.	60	IN	CNAME	stokito.duckdns.org.
stokito.duckdns.org.	60	IN	A

;; Query time: 223 msec
;; WHEN: Sun May 05 14:22:29 EEST 2019
;; MSG SIZE  rcvd: 133

You can see that router.stokito.com was firstly resolved to CNAME stokito.duckdns.org. which then was resolved to my router’s IP This have a downside that now your router’s IP is visible to anyone who would like to hack you.

Fortunately I using CloudFlare which works like a proxy that protects my site from DDoS. It’s free plan allows almost everything that I need. But what is important that I can transfer my domain to CF nameserver and CF allows to map CNAME to root domain stokito.com. So in CF DNS Settings I set the CNAME and now when I try to open stokito.com then it opened my website from the router. In fact, they don’t do a real alias and stokito.com domain refers to CF IP address but internally they proxy HTTP requests to stokito.duckdns.org.

CludFlare DNS settings screenshot
CludFlare DNS settings screenshot

So I configured these domains:

  1. router.stokito.com is a CNAME to stokito.duckdns.org and please note that the cloud icon is gray which means that CF will not proxy this domain and it will work only as DNS. Thus the router.stokito.com will be always resolved to my router’s IP via DDNS stokito.duckdns.org as you already saw before in dig command output.
  2. Wildcard * domain i.e. any other subdomain will be also resolved to my router’s IP. In fact you don’t need this, I just wanted to show that you have such possibility.
  3. The root domain stokito.com and its subdomain www will be proxied (i.e. orange cloud icon) to stokito.duckdns.org. The real IP of my router is hidden in this case and it’s protected form DDoS by CF.

Now you can check that root domain stokito.com is resolved to CF proxy:

$ dig stokito.com

; DiG 9.11.5-P1-1ubuntu2.3-Ubuntu stokito.com
;; global options: +cmd
;; Got answer:
;; HEADER opcode: QUERY, status: NOERROR, id: 35463
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

; EDNS: version: 0, flags:; udp: 4096
;stokito.com.			IN	A

stokito.com.		3600	IN	A
stokito.com.		3600	IN	A

;; Query time: 51 msec
;; WHEN: Sun May 05 14:05:34 EEST 2019
;; MSG SIZE  rcvd: 94

The IP addresses and belongs to CloudFlare.

Configure uhttpd webserver to work with the dynamic domain

In fact, you can just use the DDNS directly in /etc/config/uhttpd instead of IP address i.e.:

config uhttpd homepage
  option realm homepage
  list listen_http 'stokito.duckdns.org:80'
  option home '/tmp/www/stokito.com'
  option rfc1918_filter '0'

Here I configured my homepage on 80 port but instead of my external IP address I just used my DDNS stokito.duckdns.org. It’s important that while my domain is stokito.com it refers to CloudFlare so I can’t use it and I have to use the DDNS.

When eth1 (i.e. wan) network interface is restarted it may receive a new IP. So we have to update our DDNS. We can add a hook on iface up and send the update. So we should trigger the same command that we put into cron. To do so you need to add a hook to /etc/hotplug.d/iface/96-update-ddns.sh:

case "$ACTION" in

I set it’s prio to 97 to run it after 95-ddns script if you decided to use it instead of self made cron script. Just to avoid conflicts.

To restart uhttpd after external IP was changed you can add the hotplug script:

case "$ACTION" in
/etc/init.d/uhttpd enabled && sleep 30 && /etc/init.d/uhttpd restart

And put it to /etc/hotplug.d/iface/97-homepage.sh. We set 30 seconds delay to be sure that dns record was updated.

Now let’s try:

# ifconfig eth1 down
# ifconfig eth1
eth1      Link encap:Ethernet  HWaddr 00:C5:F4:71:1B:9A  
          BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:2488344 errors:0 dropped:499 overruns:0 frame:0
          TX packets:818007 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:3068100023 (2.8 GiB)  TX bytes:84736706 (80.8 MiB)
# ifconfig eth1 up
# ifconfig eht1
eth1      Link encap:Ethernet  HWaddr 00:C5:F4:71:1B:9A  
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::2c5:f4ff:fe71:1b9a/64 Scope:Link
          RX packets:2487401 errors:0 dropped:499 overruns:0 frame:0
          TX packets:817808 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:3068008637 (2.8 GiB)  TX bytes:84672103 (80.7 MiB)

# ps | grep uhttpd
 3007 root      1296 S    /usr/sbin/uhttpd -f -h /www -r main -x /cgi-bin -p
 3008 root      1296 S    /usr/sbin/uhttpd -f -h /tmp/www/stokito.com -r homepage1 -p stokito.duckdns.org:80
 3018 root      1200 S    grep uhttpd


  1. Stop eth1 interface. At this moment internet goes down.
  2. See eth1 details to be sure that there is no external IP.
  3. Start eth1 with ifconfig eth1 up and see it’s details that IP now obtained.
  4. Check that utthpd process is restarted after 5 seconds. To ensure that it was restarted you can change site name or realm in /etc/confg/uhttpd and then see that the name was changed after restart. Here for example you might note that I changed homepage realm name to homepage1.

In fact, we don’t have to restart the uhttpd if IP wasn’t changed. Also if we detected IP change then we can start uhttpd with the new IP. For example we can update it with uci. It’s not so easy to get ip from interface name but you can see getLocalIp function from ddns scripts dynamic_dns_functions.sh.

But this solution is much simpler so I decided to keep it.

Protect router from hackers: allow access to HTTP server only to CloudFlare proxy IPs

Since my website is accessible only from CloudFlare so I need to allow CF IPs but deny any others. I denied access to 80 port from /etc/config/firewall file but to allow CF IPs you need to add this script to /etc/firewall.user:

for ip in `wget -qO- http://www.cloudflare.com/ips-v4`; do
  iptables -I INPUT -p tcp -m multiport --dports http,https -s $ip -j ACCEPT

The script will fetch a list of CF IPs and allow them via iptables.