Does the ARP Protocol Have a Port Number?

Search for “ARP protocol port number” and you’ll find a surprising number of confidently wrong answers — some list port 67, others guess at a made-up value, and plenty of certification study guides use this exact question as a trick to catch students who assume every protocol works the same way. The real answer is simpler than any of those guesses: ARP doesn’t have a port number at all, because port numbers aren’t a concept that applies to it. This article explains why that’s the case, how ARP frames are actually identified without one, how to spot ARP traffic yourself in a packet capture, where ARP fits on a broader list of protocols and their port numbers (or lack thereof), and how to handle this exact question if it comes up on a certification exam.

Why ARP Doesn’t Use a Port Number

Port numbers exist to distinguish between different applications or services running on top of TCP or UDP at the Transport Layer — but ARP doesn’t operate at that layer at all, which is the entire reason it has no port number to speak of.

1. Port numbers are a Transport Layer (Layer 4) concept. TCP and UDP use port numbers to direct incoming data to the correct application or service on a device — for example, port 443 for HTTPS traffic or port 53 for DNS. This system only exists within protocols built on top of TCP or UDP.
2. ARP operates at the Data Link Layer (Layer 2), not the Transport Layer. As covered in earlier discussions of how ARP resolves IP addresses to MAC addresses, ARP’s entire function takes place below the Network layer where IP operates — meaning it’s even further removed from the Transport layer than IP itself.
3. ARP is encapsulated directly inside an Ethernet frame, not inside an IP packet. Because it doesn’t rely on IP for delivery, it also has no need for the TCP/UDP header structure that carries port numbers — ARP messages go straight from the Data Link layer’s Ethernet framing without ever touching a Transport-layer header.
4. Without a Transport Layer presence, there’s simply nothing for a port number to attach to. Asking “what port does ARP use” is a bit like asking what zip code a phone call uses — it’s a reasonable-sounding question built on a category error, since the concept it’s asking about doesn’t apply to the layer ARP actually operates at.

If ARP doesn’t use a port number to identify itself, though, something else has to let Ethernet know that a given frame is carrying an ARP message rather than, say, an IP packet — and that’s exactly the role played by the EtherType field, covered next.

EtherType 0x0806 vs. Port Numbers: How Protocols Are Actually Identified

Since port numbers only apply within TCP/UDP, ARP is identified using a completely different mechanism built into the Ethernet frame header itself. Here’s how the two identification systems compare.

The takeaway: where a Transport-layer protocol like HTTP relies on a port number to specify which application should handle the data once it arrives, ARP is identified far earlier in the process — the moment a device reads the Ethernet frame header, the EtherType value of 0x0806 immediately tells it “this is an ARP message,” with no need to unpack an IP packet or look for a port at all. This is also exactly the field you’d look for if you wanted to isolate ARP traffic yourself in a packet capture.

Capturing and Inspecting ARP Frames in Wireshark

Seeing the EtherType field in action is one of the clearest ways to understand how ARP identification actually works — and Wireshark makes this straightforward to observe directly.

1. Open Wireshark and select the correct network interface. Choose the interface currently handling your traffic (typically your active Wi-Fi or Ethernet adapter) and start a live capture.
2. Generate some ARP traffic to capture. On most systems, simply pinging another device on your local network, or clearing your ARP cache and then accessing a local resource, will trigger a fresh ARP request and reply.
3. Apply a display filter to isolate ARP traffic. In the filter bar at the top of Wireshark, type:

arp

This filters the capture down to only ARP request and reply frames, hiding all other traffic types. 4. Select an ARP frame to inspect it. Click on any listed ARP packet, then expand the Ethernet II section in the packet details pane below. 5. Locate the EtherType field. Within the Ethernet II header details, you’ll see a field labeled Type, showing the value 0x0806 — this is the exact mechanism discussed in the comparison above, visible in real captured traffic. 6. Expand the Address Resolution Protocol section. Below the Ethernet header, Wireshark breaks down the ARP-specific fields, including the opcode (request or reply), sender/target MAC addresses, and sender/target IP addresses — letting you directly observe the request-and-reply exchange in action. 7. Compare against a non-ARP frame for contrast. Click on a regular IPv4 packet in the same capture and check its EtherType field — you’ll see 0x0800 instead, confirming how Ethernet distinguishes between protocol types using this field rather than anything resembling a port number.

Seeing the absence of a TCP/UDP header entirely in an ARP frame — and the presence of the EtherType field doing the identification work instead — makes the Layer 2 vs. Layer 4 distinction covered earlier far more concrete than reading about it alone.

Common Protocols and Their Port Numbers (Including Protocols With None)

With ARP’s situation now clear, it helps to see where it fits alongside other common protocols — some of which use well-known ports, and some of which, like ARP, don’t use port numbers at all.

• HTTP — Port 80 (TCP): Standard unencrypted web traffic.
• HTTPS — Port 443 (TCP): Encrypted web traffic, now the default for most websites.
• DNS — Port 53 (TCP/UDP): Domain name resolution; typically UDP for standard lookups, TCP for larger responses or zone transfers.
• FTP — Ports 20 and 21 (TCP): File transfer; port 21 for control commands, port 20 for the actual data transfer.
• SSH — Port 22 (TCP): Secure remote command-line access.
• Telnet — Port 23 (TCP): Unencrypted remote access, largely deprecated in favor of SSH.
• SMTP — Port 25 (TCP): Sending email between mail servers.
• DHCP — Ports 67 and 68 (UDP): Automatic IP address assignment; port 67 for the server, port 68 for the client.
• ARP — No port number: As covered throughout this article, ARP operates at Layer 2 using EtherType 0x0806, bypassing the Transport layer entirely.
• ICMP — No port number: Used for diagnostic messages like ping; like ARP, ICMP doesn’t use TCP or UDP, though it does operate at Layer 3 (Network) rather than Layer 2, identified instead by a protocol number within the IP header rather than an EtherType field.

Keeping ARP and ICMP grouped mentally as “no-port protocols,” but for different layer-related reasons, is a useful distinction to hold onto — and it’s exactly the kind of distinction that certification exams like to probe directly, which brings us to the practice questions this topic most commonly generates.

ARP Port Number: Certification Exam Practice Questions

Because “what port does ARP use” is such a common trick question on exams like CompTIA Network+ and CCNA, it’s worth being ready for a few different ways it can be phrased.

Q: What port number does ARP use? A: None. ARP does not use a TCP or UDP port number, since it operates at Layer 2 (Data Link) and doesn’t rely on the Transport layer at all, as detailed earlier in this article.

Q: At which OSI layer does ARP operate? A: Layer 2, the Data Link layer — this is the underlying reason it has no port number, since port numbers are strictly a Layer 4 concept.

Q: How is an ARP frame identified within an Ethernet frame? A: By the EtherType field in the Ethernet header, set to 0x0806 for ARP — as shown in the comparison table and confirmed via packet capture earlier in this article.

Q: True or false — like DNS, ARP can use either TCP or UDP depending on the situation. A: False. This is a common distractor answer choice; ARP doesn’t use TCP or UDP at all, unlike DNS (Port 53) which genuinely does use both depending on the query type.

Q: Which other common protocol also has no assigned port number, and why? A: ICMP. Like ARP, it bypasses TCP/UDP entirely — though for a different reason, since ICMP operates at Layer 3 and is identified via a protocol number in the IP header rather than an Ethernet-level EtherType field, as noted in the protocol list above.

Q: If a question asks for ARP’s “port number” as a multiple-choice option, and 67, 68, 806, and “N/A” are listed, which is correct? A: “N/A” (or an equivalent “none” option) is correct. Port 67/68 belongs to DHCP, and 806 is a common decoy referencing ARP’s EtherType value in decimal rather than an actual port number — a frequent trap in exactly this kind of question.

Between understanding why ARP skips the Transport layer entirely, how EtherType handles identification in its place, what that looks like in an actual packet capture, where ARP sits alongside protocols that do use ports, and how to handle the exam questions built around this exact confusion, there’s no ambiguity left: ARP simply doesn’t have a port number, and now you know precisely why.

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