ARP Packet ARP

An address resolution request or reply, sized for Ethernet hardware addresses and IPv4 protocol addresses.

Reading a capture

Fixed length, no payload, and nothing stacks below it. That makes it the only complete lane at the bottom of a chain on this site — everything else down here ends in a slot waiting for something.

Subfields

• Hardware Type — What kind of hardware address is being resolved.
• Protocol Type — What kind of protocol address is being resolved.
• Hardware Address Length — Octets per hardware address. Six for Ethernet.
• Protocol Address Length — Octets per protocol address. Four for IPv4.
• Operation — Whether this is the question or the answer.
• Sender Hardware Address — The sender's MAC address.
• Sender Protocol Address — The sender's IPv4 address.
• Target Hardware Address — The address being asked for. All zeroes in a request, because not knowing it is the reason for sending.
• Target Protocol Address — The IPv4 address whose hardware address is wanted.

Where it sits

ARP Packet

• Open in the explorer — ARP request in a QoS Data frame

Accuracy

Clause

RFC 826

Byte order

big-endian — network byte order

Verified

Not verified against the standard. Treat this as a claim, not a fact.