Hi All,
Does any one have success of setting up Dynu ddns on Openwrt router.
If answer is yes could you point me how to do this.
Thanks freetnk

At first, sorry for my English but I try to answer...
First, add your domain in Dynamic DNS Services menu in dynu.com portal.
The next step is to add service DDNS in your OpenWRT router system. I use OpenWRT with LuCI. In GUI, in Services/Dynamic DNS, I added new service named eg "dynu". In Basic Settings tab, in field named "DDNS Service Provider" you must choose "own" or "other" and in field "Custom address update" enter link "http://api.dynu.com/nic/update?username=[USERNAME]&password=[PASSWORD]". In field "Hostname/Domain" enter your domain name which you entered in dynu.com portal. Of course, fields username and password should be entered.
In Advanced settings tab, I set 1) IP address source=URL 2) URL to detect=http://checkip.dynu.com 3) Enter network=WAN. Other fields are optional.
With this configuration my router check and update IP address.
This configuration you can see in file /etc/config/ddns
This is a part of that file:
config service 'dynu'
option domain 'yourdomain.dynu.com'
option username 'your_name_in_dynu.com'
option interface 'wan'
option use_syslog '2'
option use_logfile '1'
option ip_source 'web'
option ip_url 'http://checkip.dynu.com'
option update_url 'http://api.dynu.com/nic/update?username=[USERNAME]&password=[PASSW
ORD]'
option password 'your_password_in_dynu.com'
option enabled '1'

I just changed the UPDATE URL for just one domain:
http://api.dynu.com/nic/update?hostname=mmmmxxx.com&password=PASSWORD

It worked. Thank you.

On a router running on OpenWrt release 19.07.8 for "ath79", I got the following config to work, after the installation of package wget. cowperson is my dynu.com username, cowpassword my password, and cowsubdom.ddnsfree.com my subdomain (all made up for this illustration):

QUOTE
config service 'ddnsfree_ipv4'
option lookup_host 'cowsubdom.ddnsfree.com'
option username 'cowperson'
option password 'cowpassword'
option interface 'wan'
option service_name 'dynu.com'
option domain 'cowsubdom.ddnsfree.com'
option enabled '1'
option ip_source 'web'
option ip_url 'http://checkip.dynu.com'
UNQUOTE

Some notes to save you grief if you are a totaly newbie like me:
- How to enter the QUOTEd block into /etc/config/ddns: SSH into router, `# vi /etc/config/ddns`, "Insert" key to start editing, enter block (using your subdomain etc.), "Esc" key followed by `:wq` to save and quit. Make sure the line break is Linux style (not Windows). I don't know what cutting and pasting from this Web page does to the line break.
- `config service`: this line does not like a dash or period in its value.
- `option lookup_host` and `option domain`: Said to be the same in typical situations.
- `option service_name 'dynu.com'`: I believe it is a reference to dynu.com as service provider (whatever your subdomain may be). OpenWrt seems to have a list of service providers it "knows something" about. To see the list, use LuCI's "DDNS Service provider (IPv4)" item (more on how to get to this later).
- `option ip_source 'web'` and `option ip_url 'http://checkip.dynu.com'`:
: These are saying, "I want to get my public IP from a Web page, and the Web page to use is http://checkip.dynu.com." Set this way, ddns works even if your OpenWrt router sits behind another router (e.g. the one build into your modem).
: Alternative lines would be `option ip_source 'network'` and `option ip_network 'wan'`. These say, "I want to use the IP of my router's WAN side." Obviously this would not work if your OpenWrt sat behind another router.
- wget:
: Needed for ddns to go out to the Internet (for http://checkip.dynu.com). I suspect that je23's config would have needed wget too. Package curl is said to be an alternative to wget (I have not tested).
: To install wget, SSH into the router, `# opkg update`, `# opkg install wget`
- LuCI:
: When you enter a block into /etc/config/ddns, LuCI reflects it here: LuCI > Services > Dynamic DNS.
: For the list of "known" ddns service provides, click "Edit" for either "myddns_ipv4" (a template) or any ddns entry you already have and see the popup list for "DDNS Service provider (IPv4)."
: A bug in LuCI. "Edit" a ddns entry, go to "Advanced Settings" tab, find "IP address source [IPv4]" item, set it to "Network" (I believe this corresponds to `option ip_source 'network'`), hit "Save and Apply." You will (may) see the "IP address source [IPv4]" item revert to "URL" (corresponding to `option ip_source 'web'`). As is in the nature of a bug, it may not happen to you.
- More info: https://openwrt.org/docs/guide-user/services/ddns/client

I want to add that all the `option` line should be left-indented. Somehow the uploading process seems to have removed all the tabs.