The 14-byte Ethernet header:
<pre>
 0: ethernet destination address
 6: ethernet source address
12: ethernet type (0x0800 is IP, 0x0806 is ARP)
</pre>

The 20-byte IP header:
<pre>
 0: IP header length and version (usually 0x45)
 1: IP type of service
 2: IP length
 4: IP ID
 6: IP fragment offset
 8: IP time-to-live
 9: IP protocol (0x06 is TCP, 0x11 is UDP, 0x01 is ICMP)
10: IP checksum
12: IP source address
16: IP destination address
</pre>

The ARP packet:
<pre>
0: hardware address format (always 1)
2: protocol address format (always 0x0800)
4: length of hardware address (always 6)
6: length of protocol address (always 4)
7: operation (1 is request, 2 is reply)
8: sender's ethernet address
14: sender's IP address
18: target ethernet address
24: target IP address
</pre>