# iptables -A FORWARD -m state --state NEW -m mac --mac-source 00:DE:AD:BE:EF:00 -j ACCEPT
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$ ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 00:0C:29:E2:2B:C1  
          inet addr:192.168.0.41  Bcast:192.168.0.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:132893 errors:0 dropped:0 overruns:0 frame:0
          TX packets:17007 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:46050011 (43.9 Mb)  TX bytes:1601488 (1.5 Mb)
          Interrupt:10 Base address:0x10e0
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$ ping -c 1 192.168.0.61
$ /sbin/arp 192.168.0.61 | awk '{print $3}'
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#!/bin/sh
ping -c $1 >/dev/null && /sbin/arp $1 | awk '{print $3}' | grep -v Hwaddress
