wifi_uplink脚本分析

~ >: vim apps/tools/wifi_uplink 
#!/bin/sh
# Copyright (C) 2012 GuoWenxue <guowenxue@gmail.com QQ:281143292>
# This Shell scripts used to NAT by iptables, to make wlan0 as the downlink device
# and set the uplink device as eth0/ppp0, it will be called by crond

DOWNLINK_DEV="wlan0"

#可以改为ppp0

DEF_UPLINK_DEV="eth0"

#使能profile和ifcfg-wlan0文件
source /etc/profile
source $network_cfg_dir/ifcfg-$DOWNLINK_DEV

#在ifcfg-wlan0文件中有设置是否使用AP模式，如果没有就会在这里退出。
if [ $WORKMODE != AP ] ; then
   echo "$DOWNLINK_DEV doesn't work as AP mode, exit now..."
   exit
fi

#求出子网的网络地址，例如wlan0的子网的ip=192.168.2.1
NETWORK=`/bin/ipcalc -n $IPADDR_AP $NETMASK_AP`
DOWNLINK_SUBNET=${NETWORK##*=}


#set -x

#取得默认网关的网卡
#Current defaulte gateway out-going interface
cur_gateway_inf=`ip route show | grep default | sed -n '1p' | awk -F "dev" '{print $2}'`


#Current Uplink interface
cur_uplink_inf=`iptables -t nat -vnL POSTROUTING | grep $DOWNLINK_SUBNET | awk '{print $7}'`


#Initialise NAT or not


if [ ! -n "$cur_uplink_inf" ]; then
    iptables -A INPUT -i $DOWNLINK_DEV -j ACCEPT
    if [ -n "$cur_gateway_inf" ] ; then
        iptables -t nat -A POSTROUTING -s $DOWNLINK_SUBNET -o $cur_gateway_inf -j MASQUERADE
    fi
    exit
fi


if [ $cur_uplink_inf != $cur_gateway_inf ] ; then
   iptables -t nat -D POSTROUTING -s $DOWNLINK_SUBNET -o $cur_uplink_inf -j MASQUERADE
   iptables -t nat -A POSTROUTING -s $DOWNLINK_SUBNET -o $cur_gateway_inf -j MASQUERADE
fi