Port monitoring is the practice of continuously checking whether specific network ports on a server are open, accessible, and responding to requests. It verifies that services listening on those ports are operational and reachable from the network.
When you monitor a port, you typically initiate a connection attempt (often a TCP handshake or a simple probe) to that port on a target host. If the port responds within expected parameters, it's considered healthy. If the connection times out, is refused, or returns an error, the port is flagged as down or problematic.
Common ports monitored include:
| Port | Service |
|---|---|
| 80 | HTTP |
| 443 | HTTPS |
| 25 | SMTP |
| 53 | DNS |
| 3306 | MySQL |
| 5432 | PostgreSQL |
Port monitoring is essential for uptime monitoring, allowing you to detect service outages before users are affected. Combined with alerting, it enables rapid response to infrastructure issues. It differs from heartbeat monitoring, which checks application health directly, whereas port monitoring verifies network accessibility at the transport layer.
TipPort monitoring doesn't verify that a service is functioning correctly—only that the port is open and responding. Use application-level health checks for deeper validation.
Most infrastructure teams configure port monitoring for critical services: web servers, databases, load balancers, and mail servers. Use monitoring tools to run periodic checks from multiple geographic locations or vantage points to catch routing and regional connectivity issues.