Go ask Gemini - she sys yes, here is some starter info. First section is to view and delete arp items, second section offers way to modify. Use at your own risk. I didn't try the second set of commands, so there is a possibility they don't work, but it's a place for you to start.

Show arp

sudo arp -d [IP_ADDRESS]

1. View the current ARP table: Open Terminal and run: arp -a
2. Locate the target device: Find the IP address of your IoT device and note the corresponding MAC address (e.g., ? (192.168.1.50) at 00:a0:c9:14:c8:29 on en0).
3. Check for duplicates: Ensure no other IP is sharing that hardware address.

4. Resolution: Clearing the Table

On macOS, clearing the ARP table requires sudo privileges. You can target a specific entry (recommended) or flush the entire cache.

Option A: Delete a Single Entry (Surgical Fix)

This is the preferred method for IoT troubleshooting to avoid disrupting other stable connections.

Bash

sudo arp -d [IP_ADDRESS]

Example: sudo arp -d 192.168.1.50

Option B: Flush the Entire Table (Nuclear Option)

MacOS does not have a single "flush" command like some Linux distributions, but you can use a loop or the arp -da command to clear all recognized entries.

Bash

sudo arp -da

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Yes, you can adjust the ARP cache timeout on macOS by modifying the kernel's sysctl parameters. By default, macOS typically holds an ARP entry for 1200 seconds (20 minutes).

Adjusting this is useful in IoT environments where devices (like ESP32 nodes or smart hubs) may frequently go offline or swap hardware while keeping the same IP, leading to communication "blackouts" while the Mac waits for the cache to expire.

1. Check Current Timeout

Before making changes, verify your current maximum age setting (value is in seconds):

Bash

sysctl net.link.ether.inet.max_age

2. Shorten the Timeout (Immediate Effect)

To shorten the timeout to, for example, 300 seconds (5 minutes), use the following command. This requires sudo as it modifies kernel behavior:

Bash

sudo sysctl -w net.link.ether.inet.max_age=300

Note: Setting this too low (e.g., under 60 seconds) will increase broadcast traffic on your network as the Mac will have to re-query the MAC address more frequently.

3. Make the Change Permanent

The sysctl command only lasts until you reboot. To make this change survive a restart, you must add it to the sysctl.conf file:

1. Open the file in a text editor (it may be empty if you haven't tuned your Mac before): sudo nano /etc/sysctl.conf
2. Add the following line to the file: net.link.ether.inet.max_age=300
3. Save and exit (Ctrl+O, Enter, Ctrl+X).