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COMMAND

Test-NetConnectionTest a TCP port or host reachability

Test-NetConnection is the PowerShell cmdlet for testing network reachability. With -Port it attempts a TCP connection and reports whether the port is open, which replaces using telnet as a port tester. Without -Port it pings the host and shows the route and interface used.

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Purpose

Test-NetConnection answers "can I reach that service?" more precisely than ping. Because it opens a real TCP connection to a named port, it tests exactly what an application would do, and it works even when the host blocks ICMP so ping fails.

Testing a TCP port

powershell
Test-NetConnection example.com -Port 443
text
ComputerName     : example.com
RemoteAddress    : 93.184.215.14
RemotePort       : 443
InterfaceAlias   : Ethernet
SourceAddress    : 192.168.1.37
TcpTestSucceeded : True

TcpTestSucceeded : True means the port accepted a connection. False means closed, filtered or unreachable.

Ping and route diagnostics

powershell
Test-NetConnection example.com

Without -Port, it pings the host and reports PingSucceeded, the resolved address, and the interface and source address chosen, which is useful on multi-homed machines.

More detail

powershell
Test-NetConnection example.com -Port 443 -InformationLevel Detailed
Test-NetConnection example.com -TraceRoute

-InformationLevel Detailed adds the name-resolution results and all resolved addresses; -TraceRoute runs a route trace like tracert.

Common uses

  • Confirm a web server is listening on 443 before blaming DNS or the browser.
  • Check that a firewall change opened 3389 to a jump host.
  • Verify a mail server accepts connections on 25 from a network where outbound 25 is not blocked.
  • Diagnose a 502 by testing the proxy-to-backend port from the proxy host.

Common mistakes

  • Using it for UDP. It only tests TCP; a "False" for a UDP service is meaningless.
  • Testing from the wrong host. A port open to one network may be firewalled from another; test from where the real client sits.
  • Reading a False as "server down". Check PingSucceeded: a reachable host with a closed port is a service or firewall issue, not a connectivity one.

Older alternative

The classic telnet host port did the same TCP test but needs the Telnet client feature installed and gives a blank screen on success. Test-NetConnection is clearer and built in. See Telnet on port 23.

Frequently asked questions

Can Test-NetConnection test a UDP port?

No. It performs a TCP connect, so it works only for TCP services. UDP ports cannot be tested this way because there is no handshake; use the protocol's own client instead. See TCP vs UDP.

What does TcpTestSucceeded : False mean?

The TCP connection did not complete: the port is closed, a firewall dropped the packets, or the host is unreachable. The PingSucceeded line helps tell "host down" from "port closed on a reachable host".

Is there a shorter way to type it?

Yes: tnc host -Port 443 uses the alias. tnc host alone does a ping and route test.

Sources

Port records

Port 443 HTTPSPort 443 is the standard TCP port for HTTPS, the encrypted form of HTTP. Web browsers connect…Port 3389 RDP (Remote Desktop)Port 3389 is the default port for Remote Desktop Protocol (RDP), which gives a full graphical…Port 25 SMTP (mail relay)Port 25 is the standard TCP port for SMTP, used for server-to-server delivery of email across…Port 445 SMB (file sharing)Port 445 is the TCP port for SMB (Server Message Block) directly over TCP, used for Windows…Port 587 SMTP submissionPort 587 is the standard TCP port for message submission: a mail client sending outgoing email…Port 389 LDAPPort 389 is the standard port for LDAP, the directory protocol behind Active Directory,…Port 21 FTP controlPort 21 is the TCP port for the FTP control channel, where the client logs in and sends…Port 3306 MySQL / MariaDBPort 3306 is the default TCP port for MySQL and MariaDB database servers. Applications, ORMs…

Command records

ping Test reachability with ICMP echoping sends ICMP echo requests to a host and reports whether replies come back and how long…netstat Active connections and listening portsnetstat shows the machine's active TCP and UDP connections and the ports it is listening on.…Get-NetTCPConnection List TCP connections as objectsGet-NetTCPConnection lists the machine's TCP connections and listening ports as PowerShell…nslookup Query DNS recordsnslookup queries the Domain Name System from the command line. nslookup example.com returns…

Network fundamentals

TCP vs UDP Reliable streams versus lightweight datagramsTCP delivers a reliable, ordered byte stream over a connection established with a three-way…Port number ranges Well-known, registered and dynamic portsPort numbers run from 0 to 65535 and IANA divides them into three ranges: system or well-known…

HTTP records

HTTP 502 Bad GatewayHTTP 502 Bad Gateway means a server acting as a gateway or reverse proxy (nginx, Cloudflare, a…

Utilities

Port LookupLook up any TCP or UDP port by number or service name against the IANA registry, with links to…