Polished For Blog Post: What ARP Actually Does During a Ping. Why ARP Shows a Hostname Like private_66 When You Ping a Device
Here is a clean, polished, blog-ready rewrite — copyright-free, plagiarism-free, and integrity-safe. (ChatGPT)
Why ARP Shows a Hostname Like private_66 When You Ping a Device
When capturing network traffic, it’s common to see ARP frames that list a hostname—such as private_66—even though you’re simply pinging another device on your local network. This often surprises people, but it’s completely normal. Here’s what’s happening behind the scenes.
1. What ARP Actually Does During a Ping
When you ping an IP address on the same subnet, your machine must first know the MAC address of the destination. If that MAC address isn’t already in the ARP cache, your computer broadcasts an ARP request such as:
“Who has <target IP>? Tell <your IP>.”
That ARP broadcast includes:
- Your MAC address
- Your IP address
- The destination IP (but not its MAC)
Only after learning the target’s MAC address can your computer send the actual ICMP echo request for the ping.
2. Why Wireshark Displays the Name private_66
Although ARP uses only IP and MAC addresses, Wireshark enhances readability by resolving IP addresses into hostnames.
If your machine’s IP—say 192.168.1.66—is mapped to the local name private_66, Wireshark will label the ARP packet using that name.
This name may come from:
- Your system’s hosts file
- Local DNS
- NetBIOS or mDNS
- Any local naming service running on your network
So an ARP packet might appear in Wireshark like this:
| Field | Value |
| Source IP | 192.168.1.66 (private_66) |
| Source MAC | 00:11:22:33:44:55 |
| Destination IP | 192.168.1.1 |
| Destination MAC | ff:ff:ff:ff:ff:ff (broadcast) |
| Protocol | ARP |
The key point: ARP itself never uses hostnames—only Wireshark does.
3. What’s Really Happening Behind the Scenes
Here’s the real workflow when you ping a device on your LAN:
- ARP Request
Your system broadcasts:
“Who has 192.168.1.1? Tell 192.168.1.66.” - ARP Reply
The target responds with its MAC address. - ICMP Echo (Ping)
Now that the MAC is known, the ping packets are sent directly to the target host.
Wireshark simply displays your IP as private_66 because that name is mapped to the address.
Visual Overview
Your Machine (private_66)
IP: 192.168.1.66
MAC: 00:11:22:33:44:55
ARP Request (Broadcast)
———————————————–
Who has 192.168.1.1? Tell 192.168.1.66 (private_66)
———————————————–
Target Machine
IP: 192.168.1.1
MAC: 00:AA:BB:CC:DD:EE
Once the MAC is known → ICMP ping request goes through → ping reply returns.
Key Takeaways
- ARP is strictly Layer 2
It uses MAC addresses, not hostnames. - private_66 is only a label
Wireshark adds it for readability; the network never sends hostnames in ARP frames. - Seeing a hostname in ARP is normal
It simply means your IP has a local name defined somewhere on your system or network.
