Check the internetconnection

checkconnection.sh

Check the connection with curl or ping if not available.

restartmodem.sh

Restart any given interface of OpenWrt.

How to install on OpenWrt

Download scripts and make it executeable

Wget should be installed by default on OpenWrt. (git works as well, but it's not installed by default.)

# wget https://git.datenkastl.org/shell-scripts/checkconnection/raw/branch/main/checkconnection.sh
# wget https://git.datenkastl.org/shell-scripts/checkconnection/raw/branch/main/restartmodem.sh
# chmod +x checkconnection.sh
# chmod +x restartmodem.sh

Add restartmodem.sh as failcommand

Open checkconnection

# vi checkconnection.sh

and add the path to your restartmodem.sh at failcommand=

Install curl if desired

# opkg update
# opkg install curl

Add cronjob

Open crontab

# crontab -e

and add vor example

*/1 * * * *     /root/scripts/checkconnection.sh > /dev/zero*

to check the connection every minute and restart the modem if the check fails.