if-post-up-source-route.sh

#!/bin/sh -e
#this script requires a routing table named $IFACE (ie. bond0) exists in /etc/iproute2/rt_tables
#the $IFACE routing table is used to place the default route in for the source routing table
#ip route list table $IFACE will list the routing table for this interface

set_netinfo() {
	IPADDR=$(ifconfig "$IFACE" | grep 'inet addr:' | cut -d: -f2 | awk '{ print $1}')
	NETMASK=$(ifconfig "$IFACE" | grep 'inet addr:' | cut -d: -f4 | awk '{ print $1}')

  OLDIFS=$IFS
	IFS=.
	set -- $IPADDR
	local IPADDR1=$1
	local IPADDR2=$2
	local IPADDR3=$3
	local IPADDR4=$4

	set -- $NETMASK
	local NETMASK1=$1
	local NETMASK2=$2
	local NETMASK3=$3
	local NETMASK4=$4
	IFS=$OLDIFS
	NETWORK=$(printf "%d.%d.%d.%d\n" "$((IPADDR1 & NETMASK1))" "$((IPADDR2 & NETMASK2))" "$((IPADDR3 & NETMASK3))" "$((IPADDR4 & NETMASK4))")
	GATEWAY=$(printf "%d.%d.%d.%d\n" "$((IPADDR1 & NETMASK1))" "$((IPADDR2 & NETMASK2))" "$((IPADDR3 & NETMASK3))" "$(((IPADDR4 & NETMASK4)+1))")
}

set_netinfo
ip route flush table "$IFACE"
ip route add "$NETWORK/$NETMASK" dev "$IFACE" proto kernel scope link table "$IFACE"
ip route add default via "$GATEWAY" dev "$IFACE" table "$IFACE"
ip rule del lookup "$IFACE" || true
ip rule add from "$NETWORK/$NETMASK" lookup "$IFACE"