Port 123 · NTP

Port 123 is NTP, UDP.

Network Time Protocol — time sync for all systems. Kerberos requires clock skew under 5 minutes or authentication will fail.

Palo Alto

Create the service object for this port, then allow the App-ID on it. Restricting the rule to the port's service object keeps the rule working on a non-default port and stops the App-ID matching on other ports. Replace the placeholders with your own rule name and zones.

set service udp-123 protocol udp port 123

set rulebase security rules <rule-name> from <from-zone> to <to-zone> source any destination any application ntp service udp-123 action allow

Risk and exposure

Rated low risk. Even so, only expose this port to the networks and hosts that need it, and keep it patched.

Check it

• Linux ss -ulnp | grep :123
• nmap nmap -sU -p 123 <host>

Related ports

• 88 Kerberos
• 464 Kerberos kpasswd
• 143 IMAP
• 873 rsync
• 993 IMAPS

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