[NCLUG] Teaching dhclient to lie.

[John Gilmore]

I recently got three laptops, and want them all to have static IP addresses
on my home wireless. Unfortunately, the router doesn't support dynamically
assigning static IP's. Also, I want to keep networkmanager running so that
my wife can easily connect to wifi wherever she goes using the handy-dandy
little gnome widget.

So, I came up with a way to make it work anyway. I'll include the script,
which I put in as
/etc/dhcp3/dhclient-enter-hooks.d/static-route-on-local-wireless

I just wanted to ask if any of you knew a better way to do this, or if this
will cause other sorts of problems that I haven't noticed yet. It does seem
to be working fine so far.

The reason I ask this is that I noticed that the output from dhclient still
lists the router assigned IP address:
Listening on LPF/wlan0/00:14:d1:46:13:02
Sending on   LPF/wlan0/00:14:d1:46:13:02
Sending on   Socket/fallback
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 4
DHCPOFFER from 192.168.1.1
DHCPREQUEST on wlan0 to 255.255.255.255 port 67
DHCPACK from 192.168.1.1
192.168.1.52
bound to 192.168.1.103 -- renewal in 38828 seconds.

the ".52" is from /etc/hots, the ".103" is the router assigned address. The
router assigned address is the only one echoed, the ".52" address wouldn't
show up at all, but my script leaks it (the "echo | grep" bit echos to
console, I forgot the >/dev/null on the end)

Here's the script, so you know what I'm talking about. With this script on
each laptop, and the same hosts file, I'll just need to set the hostname
properly.

# $Id: static route on local wireless ,v 1.2 2010/10/01 jgilmore

ESSID_MINE=linksys_OW_25001
INTERFACE_MINE=wlan0

case "$reason" in
        BOUND|RENEW|REBOOT)
        if [ "$interface" = "$INTERFACE_MINE" ]; then
                #Check. If ESSID has been set to our local ESSID, create a
static
                # IP
                /sbin/iwconfig "$interface" | grep "linksys_OW_25001"
>/dev/null
                if [ $? -eq "0" ]; then
                        #Find our hostname in /etc/hosts, and try to grab
our ip address.
                        hostname=`cat /etc/hostname`
                        IP_MINE=`cat /etc/hosts | grep $hostname | sed
's/.*\(192\.168\.[0-9]\{1,3\}\.[0-9]\{1,3\}\).*/\1/'`
                        if echo $IP_MINE | grep
'192\.168\.[0-9]\{1,3\}\.[0-9]\{1,3\}'; then
                                #Lie about the dhcp response we got.
                                logger "the script in
/etc/dhcp3/dhclient-enter-scripts.d/static-route-on-local-wireless just lied
about dhclient assigned IP addresses."
                                logger "The assigned ip address was
$new_ip_address, but we're going to use $IP_MINE"
                                new_ip_address=$IP_MINE
                        else
                                #Failed to automatically determine static IP
address.
                                logger "The automatic IP fetching scheme
failed for
/etc/dhcp3/dhclient-enter-scripts.d/static-route-on-local-wireless, we got
$IP_MINE, using assigned $new_ip_address"
                        fi
                fi
        fi
        ;;
esac