通过ping获取URL的IP地址，使用iptables进行端口NAT转发

2023年5月21日 1237点热度 1人点赞 0条评论

使用ping获取指定URL的IP地址，使用iptables进行NAT转发，使用Cron进行定时检查IP是否发生改变，理论上其他系统也同样支持本文方式。

转载请注明出处，本文仅用于学习交流，不对之处，恳请指正，部分图片摘取网络，如有侵权请联系

1. 系统环境

Debian 11
iptables v1.8.7 (nf_tables)

2. 环境配置

本文使用的是iptables进行端口转发，你也可以使用ufw等工具，我在其他文章中也有大概提及使用UFW防火墙进行端口转发方式

Debian系统安装iptables iputils

sudo apt-get update && apt-get install iptables iputils-ping

CentOS7, OpenEuler安装iptables iputils
```
sudo yum install iptables iputils
```
CentOS8, OpenEuler安装iptables iputils
```
sudo dnf install iptables iputils
```

3. 脚本代码

请根据实际情况对一些代码进行调整

local_port # 你要访问的本机端口号

remote_url # 你要NAT的目标URL地址

remote_port # 你要NAT的目标端口
至于为什么用英文注释，特殊处理罢了

编写脚本
```
nano /etc/cron.d/iptablesnat.sh
```

写入以下代码

#!/bin/bash

current_time(){
    echo `date -d "@$(( $(date +%s) ))" +%Y/%m/%d' '%H:%M:%S`
}

get_internal_ip() {
    # Check for 10.x.x.x IP address
    ip_addr=$(ip addr show | grep -oP "(?<=inet\s)10(\.\d+){3}")
    if [[ -n $ip_addr ]]; then
        echo "$ip_addr"
        return
    fi

    # Check for 172.x.x.x IP address if 10.x.x.x IP address is not found
    ip_addr=$(ip addr show | grep -oP "(?<=inet\s)172\.(1[6-9]|2[0-9]|3[0-1])(\.\d+){2}")
    if [[ -n $ip_addr ]]; then
        echo "$ip_addr"
        return
    fi

    # Check for 192.168.x.x IP address if 10.x.x.x and 172.x.x.x IP addresses are not found
    ip_addr=$(ip addr show | grep -oP "(?<=inet\s)192\.168(\.\d+){2}")
    if [[ -n $ip_addr ]]; then
        echo "$ip_addr"
        return
    fi
}

internal_ip=$(get_internal_ip)

if [[ -n $internal_ip ]]; then
    echo "Internal IP Address: $internal_ip"
else
    echo "No internal IP address found."
    exit 1
fi

# Port number to use, it is recommended to use special ports like 443 or 3389 to avoid suspicion
local_port=change_to_your_port

# The remote URL address to forward to
remote_url=change_to_your_url

# The remote port to forward to, usually 443
remote_port=change_to_your_prot

# Path to save the log file
log_file="/var/log/iptablesnat.log"

# Path to save the IP address obtained from the URL
old_ip_file="/var/log/iptablesnat.oldip"

echo "===================IPTABLES===================" >> $log_file

if [ ! -f "$old_ip_file" ];then
    touch $old_ip_file
    echo "$(current_time) [I] Created IP file" >> $log_file
fi

realIP=$(ping $remote_url -c 1 -w 1 | sed '1{s/[^(]*(//;s/).*//;q}')
echo "$(current_time) [I] Current IP: $realIP" >> $log_file
oldIP=`cat $old_ip_file`
echo "$(current_time) [I] Old IP: $oldIP" >> $log_file
if [[ "$realIP" == "$oldIP" ]];then
    echo "$(current_time) [I] Current IP same as old IP, skipping..." >> $log_file
else
    if [ -n "$oldIP" ]; then
        remote=$oldIP
        echo "$(current_time) [W] Delete the old iptables rules..." >> $log_file
        iptables -t nat -D PREROUTING -p tcp --dport $local_port -j DNAT --to-destination $remote:$remote_port
        iptables -t nat -D PREROUTING -p udp --dport $local_port -j DNAT --to-destination $remote:$remote_port
        iptables -t nat -D POSTROUTING -p tcp -d $remote --dport $remote_port -j SNAT --to-source $internal_ip
        iptables -t nat -D POSTROUTING -p udp -d $remote --dport $remote_port -j SNAT --to-source $internal_ip
    fi

    remote=$realIP
    echo "$(current_time) [W] Create the new iptables rules..." >> $log_file
    iptables -t nat -A PREROUTING -p tcp --dport $local_port -j DNAT --to-destination $remote:$remote_port
    iptables -t nat -A PREROUTING -p udp --dport $local_port -j DNAT --to-destination $remote:$remote_port
    iptables -t nat -A POSTROUTING -p tcp -d $remote --dport $remote_port -j SNAT --to-source $internal_ip
    iptables -t nat -A POSTROUTING -p udp -d $remote --dport $remote_port -j SNAT --to-source $internal_ip

    echo "=======================================" >> $log_file
    echo "$(iptables -t nat -L -n --line-numbers)" >> $log_file
    echo "=======================================" >> $log_file

    echo "$(current_time) [W] Save current IP to the log file" >> $log_file
    echo $remote > $old_ip_file
    echo "$(current_time) [I] Completed!" >> $log_file
fi

4. 创建定时脚本

使用nano打开定时文件
```
nano /etc/crontab
```

最后加入以下代码

# Automatically obtain the IP that requires NAT from the URL
@reboot      root /etc/cron.d/iptablesnat.sh
*/15 * * * * root /etc/cron.d/iptablesnat.sh