link_detect.sh

#!/bin/sh
 
ping_test()
{
    out_iface=$1
    target=$2
    ping -q -I $out_iface -c $detect_pkt_num -w $detect_timeout $target > /dev/null
    return $?
}

route_prefix="114.114.114.0/24"
default_rt=`ip route show exact $route_prefix`

detect_target="114.114.114.114"
detect_pkt_num=3
detect_timeout=10

ip route add 114.114.114.114/32 via 192.168.200.1 dev tap2
ping_test "tap2" "114.114.114.114"
if [ $? -eq 1 ]; then
    echo $default_rt | grep "192.168.200.1"
    if [ $? -eq 0 ]; then
        ip route replace 114.114.114.0/24 via 192.168.4.1
    fi
else
    echo $default_rt | grep "192.168.200.1"
    if [ $? -eq 1 ]; then
        ip route replace $route_prefix nexthop ${default_rt#* } nexthop via 192.168.200.1
    fi
fi