SOHO Linux Router 2 ISP failover script

failover.sh

#!/bin/bash

# Set defaults if not provided by environment
CHECK_DELAY=${CHECK_DELAY:-5}
CHECK_IP=${CHECK_IP:-8.8.8.8}
PRIMARY_IF=${PRIMARY_IF:-eth2}
PRIMARY_GW=${PRIMARY_GW:-192.168.1.1}
BACKUP_IF=${BACKUP_IF:-eth1}
BACKUP_GW=${BACKUP_GW:-192.168.3.1}

# Compare arg with current default gateway interface for route to healthcheck IP
gateway_if() {
  [[ "$1" = "$(ip r g ${CHECK_IP} | sed -rn 's/^.*dev ([^ ]*).*$/\1/p')" ]]
}

CURRENT_GW_IF=$(ip r | grep default | cut -d' ' -f5)
echo Current GW = ${CURRENT_GW_IF}

# Cycle healthcheck continuously with specified delay
while sleep "$CHECK_DELAY"
do
  CURRENT_GW_IF=`ip r | grep default | cut -d' ' -f5`
  #echo "Setting ${CHECK_IP} traffic through ${PRIMARY_GW}"
  route add ${CHECK_IP} gw ${PRIMARY_GW}
  # If healthcheck succeeds from primary interface
  if ping -I "$PRIMARY_IF" -c1 "$CHECK_IP" &>/dev/null
  then
    echo "Primary interface ${PRIMARY_IF} is working"
    # Are we using the backup?
    #echo Current GW IF = ${CURRENT_GW_IF}
    #echo Backup IF = ${BACKUP_IF}
    if [ "${CURRENT_GW_IF}" == "${BACKUP_IF}" ]; then # Switch to primary
      echo "Switching from backup interface ${BACKUP_IF} to primary ${PRIMARY_IF}"
      ip r d default via "${BACKUP_GW}" dev "${BACKUP_IF}"
      ip r a default via "${PRIMARY_GW}" dev "${PRIMARY_IF}"
    fi
  else
    # Are we using the primary?
    echo "Primary interface ${PRIMARY_IF} is not working"
    if [ "${CURRENT_GW_IF}" == "${PRIMARY_IF}" ]; then # Switch to backup
      echo "Switching from primary ${PRIMARY_IF} interface to backup ${BACKUP_IF}"
      ip r d default via "${PRIMARY_GW}" dev "${PRIMARY_IF}"
      ip r a default via "${BACKUP_GW}" dev "${BACKUP_IF}"
    fi
  fi
  #echo "Deleting ${CHECK_IP} traffic through ${PRIMARY_GW}"
  route del 8.8.8.8
done