Bounce IPv6 connection if router is up but IPv6 connectivity is down, and check the connection every 30 seconds.

bounce_ipv6.sh

#!/bin/bash
# Put this script into your crontab e.g. 
# @reboot ~/bin/bounce_ipv6.sh
# Bounce IPv6 connection if router is up but IPv6 connectivity is down,
# and check the connection every 30 seconds.
router_address="192.168.0.1"
ipvsixaddress="2600::"
while true;
do
  if ping -c1 $router_address &>/dev/null; then
    if ping -c1 $ipvsixaddress &>/dev/null; then
      :
    else
      echo "Resetting ipv6 connection..."
      primary_connection=$(nmcli -t -f UUID con | head -n 1)
      sudo nmcli connection modify "$primary_connection" ipv6.method "disabled"
      sudo nmcli connection up "$primary_connection"
      sudo nmcli connection modify "$primary_connection" ipv6.method "auto"
      sudo nmcli connection up "$primary_connection"
    fi
  fi
  sleep 30
done