Port Monitoring
Continuous Port Monitoring for Your Servers
A server can stay online while the service on it silently stops responding. AlertSpy's TCP port monitoring confirms that SSH, FTP, SMTP, databases, and any custom service are actually accepting connections — not just that the host is reachable.
How AlertSpy Port Monitoring Works
A TCP handshake attempt on the specified host and port tells you whether the connection is accepted, refused, or times out — this checks connection acceptance, not application-layer correctness.
Connect to the Port
AlertSpy tries to establish a TCP connection to the host and port you've chosen. This checks whether the service is accepting, refusing, or timing out new connections.
Verify the Connection
If the service accepts the connection, the check passes. If the connection is refused or times out, AlertSpy marks the port as unavailable and records the result for that server.
Measure Response Time
Every time a port is successfully checked, AlertSpy keeps a record of the response time — so you can detect slow services before they become unresponsive.
Alert Your Team
The moment a port's status changes to unavailable, or its response time crosses a threshold you've set, AlertSpy sends alerts over Slack, Teams, and email.
Port Monitoring Made Simple
Port monitoring is built directly into AlertSpy — no separate tool, no extra setup.
Check Ports Every Minute
AlertSpy checks your ports every minute to make sure they're accepting connections. Spot service issues before they affect your users.
Monitor Multiple Ports on One Server
Keep an eye on every critical service running on the same server. View each port individually while managing everything from one dashboard.
Built-in Presets & Custom Ports
Start monitoring popular standard-port presets (22, 21, 25, 3306, 5432, 6379, and more), or enter any non-standard TCP port your applications use.
Track Port Response Times
Watch the response time of each port on your server from dedicated charts. Spot slowdowns before they become outages.
Allow Monitoring Through Your Firewall
Add AlertSpy's whitelisted checker IPs to your firewall allow list so your port monitors can connect reliably every time.
Monitor by IP or Hostname
Set up monitoring using an IP address or hostname. AlertSpy supports both IPv4 and IPv6, making it easy to monitor any environment.
Why Does Port Monitoring Show "Down" When Your Service Is Running?
If AlertSpy reports that a port is down while the service appears to be running, the service itself may not be the problem. In most cases, the issue is caused by network settings or server configuration that prevent new TCP connections from reaching the application.
A firewall or cloud security group can block incoming connections from AlertSpy's monitoring servers even while your application keeps running. Some applications are also configured to listen only on 127.0.0.1 (localhost) instead of the server's public or private network interface — in that case, the service works locally but can't accept connections from external monitors. A different process may already be bound to the port you're trying to monitor, or a firewall, load balancer, or IPS system may be rate-limiting connections from a particular IP address, causing intermittent failures.
How can you confirm the problem?
Check your firewall and security-group rules to make sure AlertSpy's checker IPs are allowed through, and verify which network interface your service is actually listening on. If you only need to confirm basic network connectivity rather than a specific service, our Ping Monitoring page covers that first step, including the ICMP-blocking issues that cause a similar "down when it's actually up" result.
How Different Teams Use Our Port Monitoring Software Every Day
From hosting providers to agencies, port monitoring scales with however many services your team is responsible for keeping online.
Hosting Providers
Customer-facing services need to be online around the clock. AlertSpy monitors every critical port on a server, and the moment a service drops or stops accepting connections, you can resolve the issue before support tickets start arriving.
DevOps Teams
A deployment may finish successfully, but a database or internal service can still fail to start. AlertSpy monitors multiple ports on a single dashboard, confirming that every critical service is accepting connections after every release.
System Administrators
Remote access is something you don't think about until it stops working. Monitor SSH, FTP, RDP, and other essential ports every minute and know immediately if one goes down, before it disrupts your team.
Agencies
Agency clients heavily depend on email for orders, support requests, and business communication. Port monitoring watches SMTP, POP3, and IMAP services and alerts you before email interruptions become a bigger problem.
Frequently Asked Questions
What's the difference between port monitoring and ping monitoring?+
Ping monitoring tells you whether a server or device is reachable over the network using ICMP. Port monitoring checks whether a specific service is accepting TCP connections on a particular port. A server can successfully respond to a ping while its web server, database, or mail service is unavailable, which is why many IT teams use both together.
How does TCP port monitoring work?+
Port monitoring attempts to establish a TCP connection to the host and port you've configured. If the connection is accepted, the check passes and AlertSpy records the response time. If the connection is refused or times out, AlertSpy marks the port as unavailable and notifies your team based on your alert settings.
Can I monitor multiple ports on one server?+
Yes. Servers often run several critical services at once, each listening on a different port. AlertSpy lets you monitor each port individually — SSH, HTTPS, databases, mail servers, and more — all from the same dashboard. Because every port has its own monitor and alert history, you'll know exactly which service has an issue instead of guessing.
Why does my port show closed when the service is running?+
More often than not, this comes down to network configuration rather than an error with the monitor itself. Common causes include a firewall or security group blocking AlertSpy's checker IP, the service listening only on 127.0.0.1 instead of the public interface, a different process already bound to the port, or connection-rate limiting on the target. Check your firewall settings and confirm which interface the service is listening on.
What ports should I monitor on a server?+
Monitor the ports that support your critical business services. Common examples include SSH (22), FTP (21), SMTP (25), DNS (53), HTTP (80), HTTPS (443), MySQL (3306), PostgreSQL (5432), and Redis (6379), plus any custom ports your applications use. The goal is to monitor the services your users and applications depend on.
Does port monitoring check if the service is working correctly, or just that it's open?+
Port monitoring verifies that a service is accepting TCP connections — it doesn't inspect the application's response, content, or business logic after the connection is established. If you need to verify HTTP status codes, page content, or API responses, combine Port Monitoring with AlertSpy's HTTP or HTTPS Monitoring.
Why choose AlertSpy Port Monitoring?+
AlertSpy supports all standard and custom TCP ports, tracks response times, handles IPv4 and IPv6, and sends immediate notifications the moment a service stops working. Because it's part of the AlertSpy platform, you can manage port monitoring alongside websites, servers, SSL certificates, domains, and ping — all from one dashboard.
Start a Free Trial Today
Monitor every critical port in real time and get notified before a small service issue turns into unexpected downtime.