NetworkManager hook to update the routing tables for dual-homed systems, allowing traffic past the gateway on either interface.

75-dual-home-routing.sh

#!/bin/bash
# 75-dual-home-routing
# Description: Updates routing tables to allow traffic on dual-homed boxes
# according to the interface it came in on
# Place in /etc/NetworkManager/dispatcher.d/ and update interface name below

IF=$1
STATUS=$2

function update_routing_table() {
  IP_ADDR=$(echo ${IP4_ADDRESS_0} | awk -F'/' '{ print $1 }')

  ip rule add from ${IP_ADDR} table 20
  ip route add default via ${IP4_GATEWAY} dev ${DEVICE_IP_IFACE} table 20
}

function clear_routing_table() {
  ip rule del lookup 20
  ip route del default via ${IP4_GATEWAY} dev ${DEVICE_IP_IFACE} table 20
}

if [ "$IF" == "eth1" ]
then
  case "$2" in
    up)
      logger -s "NM Script up triggered"
      update_routing_table
      ;;
    down)
      logger -s "NM Script down triggered"
      clear_routing_table
      ;;
    *)
      ;;
  esac
fi