Introduction

I provide here an example setup which are more complicated than your setup probably will be.

Use case

I have 1 laptop and 2 freerunners. Whenever I plug my freerunner, I want my laptop recognize which freerunner was plugged in and act accordingly. Also automagically set up the networking for me.

Prerequisites

You need a linux/unix computer with working NetworkManager setup. I have successfully use this method more than a month now, with Ubuntu 9.04 (jaunty), I will test it also on Ubuntu 8.10 (intrepid), and report back here.(I tested, and it does not work, however 9.10 works great)

Tested distributions

The NetworkManager on jaunty is:

ii  network-manager                            0.7.1~rc4-0ubuntu1 
ii  network-manager-gnome                      0.7.1~rc4.1-0ubuntu1

File/directory structure

/etc/NetworkManager/system-connections/freerunner_bob   (owner: root, rights: 600)
/etc/NetworkManager/system-connections/freerunner_bobek (owner: root, rights: 600)
/etc/NetworkManager/dispatcher.d/10myiptables           (owner: root, rights: 755)

File contents

/etc/NetworkManager/system-connections/freerunner_bob:

[connection]
id=Bob's moko
uuid=27afa607-ee36-43f0-b8c3-9d245cdc4bb4
type=802-3-ethernet
autoconnect=true
timestamp=0
[ipv4]
method=manual
never-default=true
address1=192.168.0.200;24
[802-3-ethernet]
mac-address=00:1f:11:01:5d:13  

/etc/NetworkManager/system-connections/freerunner_bobek:

[connection]
id=Bobek's moko
uuid=27afa607-ee36-43f0-b8c3-9d245cdc4bb3
type=802-3-ethernet
autoconnect=true
timestamp=0
[ipv4]
method=manual
never-default=true
address1=192.168.0.200;24
[802-3-ethernet]
mac-address=00:1f:11:01:6e:12

/etc/NetworkManager/dispatcher.d/10myiptables:

#!/bin/sh -e
# Script to dispatch NetworkManager events
#
# Runs ifupdown scripts when NetworkManager fiddles with interfaces.

# Bobek's freerunner
export MYUUID1="27afa607-ee36-43f0-b8c3-9d245cdc4bb3"

# Bob's freerunner
export MYUUID2="27afa607-ee36-43f0-b8c3-9d245cdc4bb4"

# The computer's username
export USERNAME="lolza"

if [ -z "$1" ]; then
    echo "$0: called with no interface" 1>&2
    exit 1;
fi

# Fake ifupdown environment
export IFACE="$1"
export LOGICAL="$1"
export ADDRFAM="NetworkManager"
export METHOD="NetworkManager"
export VERBOSITY="0"

# Run the right scripts
case "$2" in
    up)
	export MODE="start"
	export PHASE="up"

	if [ -f /sys/class/net/$IFACE/address ] ; then
		tmpfile=`mktemp -t`
		echo $CONNECTION_UUID > $tmpfile
		if [ "X${CONNECTION_UUID}" = "X${MYUUID1}" ] ; then
			echo "Bobek's Freerunner connected..." >> $tmpfile
			date >> $tmpfile
			iptables -A POSTROUTING -t nat -j MASQUERADE -s 192.168.0.0/24
			iptables -P FORWARD ACCEPT
			sysctl -w net.ipv4.ip_forward=1
			sudo -u ${USERNAME} ssh-keygen -R 192.168.0.202
		else
			if [ "X${CONNECTION_UUID}" = "X${MYUUID2}" ] ; then
				echo "Bob's Freerunner connected..." >> $tmpfile
				date >> $tmpfile
				iptables -A POSTROUTING -t nat -j MASQUERADE -s 192.168.0.0/24
				iptables -P FORWARD ACCEPT
				sysctl -w net.ipv4.ip_forward=1
				sudo -u ${USERNAME} ssh-keygen -R 192.168.0.202
			fi
		fi
	fi
	;;
    down)
	export MODE="stop"
	export PHASE="down"

	tmpfile=`mktemp -t`
	echo "down called..." >> $tmpfile
	tmpfile=`mktemp -t`
	echo $CONNECTION_UUID > $tmpfile
	if [ "X${CONNECTION_UUID}" = "X${MYUUID1}" ] ; then
		echo "Bobek's Freerunner disconnected..." >> $tmpfile
		iptables -D POSTROUTING -t nat -j MASQUERADE -s 192.168.0.0/24
		iptables -P FORWARD ACCEPT
		sysctl -w net.ipv4.ip_forward=0
	else
		if [ "X${CONNECTION_UUID}" = "X${MYUUID2}" ] ; then
			echo "Bob's Freerunner disconnected..." >> $tmpfile
			iptables -D POSTROUTING -t nat -j MASQUERADE -s 192.168.0.0/24
			iptables -P FORWARD ACCEPT
			sysctl -w net.ipv4.ip_forward=0
		fi
	fi
	;;
    *)
	echo "$0: called with unknown action \`$2'" 1>&2
	exit 1
	;;
esac