#! /bin/sh
#
# default_route.sh - Set default route to use specific network interface
# Copyright 2003 Tommi Saviranta <tsaviran@cs.helsinki.fi>
#
# This script is designed to set default routing to use specific network
# interface. When a default route is deleted, single-host route is added
# to the old gateway so that old routing can be restored. This means the
# script will litter your kernel IP routing table by one "useless" rule
# for each network interface that will be used as default route. If the
# script believes that something isn't going as expected, it should only
# print an error message and kernel IP routing table. The script may not
# work properly if more than one default route exists.
#
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
#
#
# Version: default_route.sh v0.1.2  24-Feb-2004  tsaviran@cs.helsinki.fi


get_field_no ()
{
	TMP=$(echo "$1" | tr -s ' ' '\t' | cut -f $2)
}


get_gateway ()
{
	get_field_no "$(route -n | grep UG | grep $1 | head -1)" 2
}



# Show usage
#
if [ $# -ne 1 ]; then
	echo "Usage: $0 INTERFACE"
	echo "Current default route:"
	route -n | head -2 | tail -1
	route -n | grep '^0.0.0.0'
	exit 0
fi


# Get current route
#
LINE=$(route -n | grep '^0.0.0.0')
get_field_no "$LINE" 8
OLDDEV="$TMP"


# See if we don't need to do a thing
#
if [ "$1" = "$TMP" ]; then
	echo "Current default route already through $1."
	exit 0
fi


# Get new gateway
#
get_gateway $1
if [ "$TMP" = "" -o "$TMP" = "0.0.0.0" ]; then
	echo "Couldn't get new gateway (got \"$TMP\")!" >&2
	route -n >&2
	exit 1
fi
NEWGATEWAY="$TMP"


# Get old default route's IP and set a static routing to it so we don't lose
# it's address. If a route to gateway already exists, skip this.
#
get_gateway $OLDDEV
if [ "$TMP" = "" -o "$TMP" = "0.0.0.0" ]; then
	echo "Couldn't get old gateway (got \"$TMP\")!" >&2
	route -n >&2
	exit 1
fi
if [ -z "$(route -n | grep UGH | grep $TMP)" ]; then
	route add -host $TMP gateway $TMP dev $OLDDEV
fi


# Delete old default route
#
get_field_no "$LINE" 2
route del default gateway $TMP dev $OLDDEV


# Set up a new gateway
#
route add default gateway $NEWGATEWAY dev $1