% - mac to ip finder


	Code	Mac Address to IP Address
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I have a wireless network at home, and the hosts are dynamically assigned IP addresses by our little WAP device.
If I'm going to connect from one host to another, it is useful to be able to find the assigned IP of the remote host.

I know the MAC address of my machines - that doesn't change. Hence, the MAC to IP finder.

If the host you are looking for isn't already in the arp cache, this script broadcast pings your segment - all hosts respond, and your local arp table fills with everyone's MAC address to IP mapping.
Then the script extracts the IP you're looking for.

You need to set the default mac to look for in MACADDR, and probably your broadcast address is different than mine - so change BCAST appropriately.
You can specify an alternative MAC on the command line like so:

./findip.sh ff:ff:ff:ff:ff:ff

To connect to the host I've configured it for, I do something like this:

$ ssh `findip.sh`

The script:

#!/bin/bash

# findip.sh
# Ben H Kram 
# 
# Finds the ip of of the host with the given mac addr
# Requires: hosts respond to pings, hosts on same segment

MACADDR="f1:f2:f3:f4:f5:f6"
BCAST=192.168.1.255

PING=/sbin/ping
ARP=/usr/sbin/arp
AWK=/usr/bin/awk
GREP=/usr/bin/grep
HEX='[[:xdigit:]]{1,2}'
PINGCOUNT=2
ECHO=/bin/echo

check_mac(){
    $ECHO $MACADDR | $GREP -E -e "($HEX:){5}$HEX" > /dev/null
    if [ $? != "0" ]; then
	$ECHO "\"$MACADDR\" is not a valid MAC address"
	exit 1
    fi
}

if [ "${1}" != "" ]; then
    MACADDR="$1"
    check_mac
fi

# check to see if it is already in the cache
IP=`$ARP -a | $GREP $MACADDR | $AWK 'BEGIN {FS = "[ \t\(\)]+" } {print $2}'`
if [ $IP != "" ]; then
    echo $IP
    exit 0
fi

$PING -c $PINGCOUNT $BCAST > /dev/null
$ARP -a | $GREP $MACADDR | $AWK 'BEGIN {FS = "[ \t\(\)]+" } {print $2}'
# eof

If you like it, use it.