ARPOpCode

• 1 for StandardARPRequest
• 2 for StandardARPResponse
• 3 or 4 for RARP - See also UnusualARPOpCode
• 8 or 9 for InverseARP - See also UnusualARPOpCode
• Anything else is malformed - See also UnusualARPOpCode
• Official list is at https://www.iana.org/assignments/arp-parameters/arp-parameters.xhtml#arp-parameters-1
• Referred to as ar$op on line 148 of RFC826