Should not be public
Port 123 — NTP
Network time synchronisation. Accurate clocks matter more than people think — TLS certificates fail on a wrong clock.
Port
123
Service
NTP
Protocol
UDP
Security guidance
Publicly reachable NTP servers are used for amplification attacks. Clients do not need an open inbound port.
Is port 123 open on your server?
Test it from outside your network — the only view that matters.
Other common ports
20 · FTP data
21 · FTP control
22 · SSH / SFTP
23 · Telnet
25 · SMTP
53 · DNS
80 · HTTP
110 · POP3
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