greddns.sh

#!/bin/bash
export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"

while getopts ":i:n:" opt; do
    case $opt in
        i)
            GRE_INTERFACE="$OPTARG"
            ;;
        n)
            DOMAIN_NAME="$OPTARG"
            ;;
        \?)
            echo "Usage: $0 -i <GRE_INTERFACE> -n <DOMAIN_NAME>"
            exit 1
            ;;
        :)
            echo "Option -$OPTARG requires an argument."
            exit 1
            ;;
    esac
done

# Check if required options are provided
if [ -z "$GRE_INTERFACE" ] || [ -z "$DOMAIN_NAME" ]; then
    echo "Usage: $0 -i <GRE_INTERFACE> -n <DOMAIN_NAME>"
    exit 1
fi

# Get the IP address from the current domain name resolution
resolved_ip=$(host -t A $DOMAIN_NAME | awk '/has address/ {print $NF}')

if [ -z "$resolved_ip" ]; then
    echo "Unable to resolve the domain name $DOMAIN_NAME"
    exit 1
fi

# Get the current remote IP address of the GRE interface
current_gre_ip=$(ip tunnel show $GRE_INTERFACE | awk '/remote/ {split($4, a, "/"); print a[1]}')

echo "Resolved IP: $resolved_ip"
echo "Current GRE IP: $current_gre_ip"

if [ "$resolved_ip" == "$current_gre_ip" ]; then
    echo "The GRE interface $GRE_INTERFACE is already configured with the IP address from the domain name resolution: $resolved_ip"
    exit 0
fi

# Update the remote IP address of the GRE interface
ip tunnel change $GRE_INTERFACE remote $resolved_ip
sed -i "s/id-remote\ =\ .*/id-remote\ =\ $resolved_ip/;s/remote_addrs\ =\ .*/remote_addrs\ =\ $resolved_ip/;/remote {/,/}/s/id = [0-9.]\+/id = $resolved_ip/" /etc/stronswan/conf.d/shzj.conf
systemctl restart strongswan-swanctl

if [ $? -eq 0 ]; then
    echo "Successfully updated the remote IP address of GRE interface $GRE_INTERFACE to: $resolved_ip"
else
    echo "Failed to update the remote IP address of GRE interface $GRE_INTERFACE"
    exit 1
fi