Port 53 · DNS

Port 53 is DNS, TCP and UDP.

Domain Name System. UDP for queries; TCP for zone transfers and responses over 512 bytes.

Palo Alto

Create the service objects 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 tcp-53 protocol tcp port 53
set service udp-53 protocol udp port 53

set rulebase security rules <rule-name> from <from-zone> to <to-zone> source any destination any application dns service [ tcp-53 udp-53 ] 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 -tlnp | grep :53
• Linux ss -ulnp | grep :53
• PowerShell Test-NetConnection <host> -Port 53
• nmap nmap -p 53 <host>
• nmap nmap -sU -p 53 <host>

Related ports

• 43 WHOIS
• 42 WINS
• 137 NetBIOS Name Service

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