Ubuntu 24.04 VM randomly disappears from LAN in Bridged mode (MacBook Pro M3 Max, Parallels 20.4.1)

Hi everyone,

I've been struggling with an issue for days and finally found a reliable fix, so I'm sharing it here.

Setup:
• MacBook Pro M3 Max (Apple Silicon)
• Parallels Desktop 20.4.1 (build 55996)
• Guest OS: Ubuntu 24.04 ARM
• Network mode: Bridged - Default Adapter

Problem:
Every 1-3 minutes, my Ubuntu VM became unreachable from the Mac host and the LAN:
• SSH and pings to the guest stopped working.
• Inside the VM everything still worked fine - Internet, outgoing pings, etc.
• If I pinged the host (from inside the VM), connectivity was instantly restored -- for a minute or two -- until it dropped again.

So the network inside the VM never actually went down -- it just stopped being visible to other devices. On the Mac, arp -a showed an "incomplete" entry for the VM's IP, so it looked like an ARP cache aging issue in Parallels Bridge mode.

Root cause (most likely):
The Parallels bridge driver seems to stop sending broadcast ARP packets when the guest is idle, so the Mac forgets its MAC mapping after a short timeout. If the guest VM doesn't transmit anything for ~60 seconds, the host drops it from the ARP table and the connection dies.

Solution:
Keep the bridge alive by sending a tiny ping from the VM to the host every 30 seconds. This forces ARP refresh without breaking anything or restarting services.

1️⃣ Create the script
sudo nano /usr/local/bin/ping_host_keepalive.sh

Paste this:
#!/bin/bash
HOST="192.168.1.18" # replace with your Mac host IP
ping -c 1 -W 2 $HOST > /dev/null

2️⃣ Make it executable
sudo chmod +x /usr/local/bin/ping_host_keepalive.sh

3️⃣ Add to cron
sudo crontab -e

Add two lines (to run every 30 seconds):
* * * * * /usr/local/bin/ping_host_keepalive.sh
* * * * * sleep 30; /usr/local/bin/ping_host_keepalive.sh


That's it. Your VM will now send a lightweight ping every 30 seconds, keeping the ARP entry active and the connection stable.

After doing this, my Ubuntu VM has been completely stable -- no more network drops, no manual resets.

⸻

If any Parallels engineers see this -- please check the bridge ARP timeout logic on Apple Silicon hosts. The guest is still alive and pingable from inside, so it shouldn't disappear from the network like that.