Port 580: SNTP heartbeat — The network's pulse check

Port 580 is officially assigned to sntp-heartbeat, a diagnostic mechanism that uses Simple Network Time Protocol packets to monitor multicast network connectivity. While SNTP normally synchronizes clocks on port 123, this variant on port 580 serves a different purpose: it proves the network is alive.

What SNTP Heartbeat Does

Every few seconds (typically five or more), an SNTP server sends a multicast packet. Clients listen. They don't reply—they just confirm they're still receiving. If the packets stop arriving, something in the multicast routing infrastructure has failed.¹

This is a heartbeat in the literal sense. A steady pulse that means "still here." When it stops, you know there's a problem.

The Genuine Utility

Network operators use this to detect multicast connectivity losses. Application developers use it to decide whether to enable multicast features or fall back to unicast. If your strategically-placed SNTP server's heartbeat disappears, you know the IP multicast routing has failed somewhere between source and destination.²

The protocol keeps bandwidth consumption minimal—under 200 bps when configured properly. Sixty-byte SNTP packets plus 28-byte IP/UDP headers, sent every five seconds or more. Just enough to prove the path exists.³

Why It Uses SNTP

SNTP was already designed for multicast operation. It uses reserved IP multicast address 224.0.1.1. It's lightweight, well-understood, and already deployed. Rather than inventing a new heartbeat protocol, the IETF proposed reusing what worked.¹

The packets even carry valid time synchronization data. Clients could use them for both purposes—keeping time and confirming connectivity. That's efficiency: one packet, two functions.

Security Considerations

Port 580 traffic should only appear from legitimate SNTP heartbeat servers on your network. If you see unexpected traffic:

# Check what's listening on port 580
sudo lsof -i :580
sudo netstat -tulpn | grep :580

# On Windows
netstat -ano | findstr :580

Because this is multicast traffic, it can traverse network boundaries if your routers are configured to forward it. Understand where your heartbeat packets should originate and where they should be received.

The Honest Reality

In practice, SNTP heartbeat is relatively obscure. Most networks use other mechanisms for monitoring multicast connectivity. The standard SNTP time synchronization on port 123 is ubiquitous—the heartbeat variant on port 580, far less so.

But the concept remains elegant: use a time protocol not to tell time, but to detect when time has stopped flowing across your network infrastructure.

Related Ports

• Port 123 - Standard SNTP/NTP time synchronization
• Port 319 - PTP (Precision Time Protocol) event messages
• Port 320 - PTP general messages