Port 88 · Kerberos

Port 88 is Kerberos, TCP and UDP.

Kerberos authentication — the backbone of Active Directory SSO. Clients request TGTs here; services validate tickets.

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-88 protocol tcp port 88
set service udp-88 protocol udp port 88

set rulebase security rules <rule-name> from <from-zone> to <to-zone> source any destination any application kerberos service [ tcp-88 udp-88 ] action allow

Risk and exposure

Rated medium risk. Restrict this port to the sources that need it and keep the service patched; avoid exposing it to the whole internet unless the service is meant to be public.

Check it

• Linux ss -tlnp | grep :88
• Linux ss -ulnp | grep :88
• PowerShell Test-NetConnection <host> -Port 88
• nmap nmap -p 88 <host>
• nmap nmap -sU -p 88 <host>

Related ports

• 464 Kerberos kpasswd
• 49 TACACS+
• 123 NTP
• 1812 RADIUS Auth
• 389 LDAP
• 636 LDAPS

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