Script check ICMP and auto change route static

[buff2l0]

Diagram:

                            GRE Tunnel ISP A
                          |------ISP A------|
Site A----FW A (Linux)----|  GRE Tunnel     |----FW B (Linux)----Site B
                          |------ISP B------|
                           GRE Tunnel ISP A 
  

Site A connect to Site B: 2 GRE Tunnel

- Site A --> GRE Tunnel ISP A --> Site B
- Site A --> GRE Tunnel ISP B --> Site B

Default routing Site A --> Site B: GRE Tunnel ISP A

The sometimes Site A --> GRE Tunnel ISP A --> Site B: packets loss, i want script checking ICMP Packet loss and change static route to GRE Tunnel ISP B.

PS: I have use monit checking ICMP but only checking host down, up.

This is my script shell:

 #! /bin/bash
 
# ping_check.sh
 
ping_check()
{
  ping_recv=`ping -W1 -f -c100 $1 | grep rtt | cut -f4 -d' ' | cut -f2 -d'/' | cut -f1 -d'.'`
  ping_loss=`ping -W1 -f -c100 $1 | grep loss | cut -f3 -d',' | cut -f2 -d' ' | sed 's/\(.*\)./\1/'`
  if [ "$ping_recv" -gt 200 ] || [ "$ping_loss" -gt 10 ]; then
   return 0 
  else
   return 1
  fi
}
 
ispa_route()
{
  ip ro re 10.10.0.0/16 dev gre_isp_a
  ip ro re 10.20.0.0/16 dev gre_isp_a
  ip ro re 10.30.0.0/16 dev gre_isp_a
 
  current_route=ispa
  echo $current_route > current_route
  echo `date` $current_route >> change_route.log
}
ispb_route()
{
  ip ro re 10.10.0.0/16 dev gre_isp_b
  ip ro re 10.20.0.0/16 dev gre_isp_b
  ip ro re 10.30.0.0/16 dev gre_isp_b
 
  current_route=ispb
  echo $current_route > current_route
  echo `date` $current_route >> change_route.log
}
 
ISPA_IP=1.1.1.1
ISPB_IP=5.5.5.5
 
ispa_route
 
while [ "1" = "1" ]; do
 case $current_route in
  ispa)
   !(ping_check $ISPA_IP) && ispb_route 
  ;;
  ispb)
   !(ping_check $ISPB_IP) && ispa_route
  ;;
  *)
 esac
 sleep 10
done 
  

[buff2l0]

Who can help me? Thanks