#!/usr/bin/bash

ifaces=($(ip link | grep '^[0-9]' | cut -d: -f2 | sed '1d;s/ //'))
iface=${ifaces[0]}
if [ $# -gt 0 ]; then
  found=0
  for i in ${ifaces[@]}; do
    if [ $1 == $i ]; then
      found=1
      break
    fi
  done
  if [ $found -eq 0 ]; then
    echo 'ERROR: invalid interface.'
    exit 1
  fi
  iface=$0
fi

ip=$(ip addr show $iface | grep inet | egrep -o '([0-9]+\.?){4}' | sed 2d)
subnet=${ip%.*}

# TODO: Adjust to network
for i in $(seq 100 254); do
  tp=$subnet.$i
  ping -w 1 -c 1 $tp &> /dev/null
  if [ $? -eq 0 ]; then
    arp=$(arp -n $tp)
    if [ $? -eq 0 ]; then
      mac=$(echo "$arp" | sed 1d | awk '{print $3}')
      if [[ "$mac" =~ ^b8:27:eb ]]; then
        echo $tp
        break
      fi
    fi
  fi
done