Never expose to the internet

Port 23 — Telnet

Q: Should port 23 be open to the internet?

Never expose to the internet. If this is open, close it today. There is no safe use for Telnet on the public internet.

Unencrypted remote shell from the era before SSH. Everything, including the password, crosses the network in plain text.

Port

Service

Telnet

Protocol

TCP

Security guidance

If this is open, close it today. There is no safe use for Telnet on the public internet.

Test port 23 yourself

From your own machine, against any host (swap in your domain):

macOS / Linux — netcat

nc -vz example.com 23

Any OS — nmap

nmap -p 23 example.com

Windows — PowerShell

Test-NetConnection example.com -Port 23

open = a service answered on port 23; closed = the host replied but nothing is listening; filtered = a firewall silently dropped the probe. These test from your network — our port checker tests from the outside, the view that matters for security.

Is port 23 open on your server?

Test it from outside your network — the only view that matters.

Check port 23

Other common ports

20 · FTP data 21 · FTP control 22 · SSH / SFTP 25 · SMTP 53 · DNS 80 · HTTP 110 · POP3 123 · NTP 143 · IMAP 161 · SNMP 389 · LDAP 443 · HTTPS 445 · SMB 465 · SMTPS 587 · SMTP submission 993 · IMAPS 995 · POP3S 1433 · Microsoft SQL Server 1521 · Oracle Database 2082 · cPanel 2083 · cPanel (TLS) 3000 · Node.js / dev server 3306 · MySQL / MariaDB 3389 · RDP 5432 · PostgreSQL 5900 · VNC 6379 · Redis 8080 · HTTP alternate 8443 · HTTPS alternate 9200 · Elasticsearch 27017 · MongoDB