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SESK: Stuff Everyone Should Know · sesk.info/secplus-kerberos-port-88

On which port do Kerberos servers (KDCs) listen for requests by default?

Port 88 (UDP and TCP) by default.

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  1. Port 88 ✔
  2. Port 389
  3. Port 443

Why: RFC 4120 says Kerberos servers should listen on port 88 unless configured otherwise. A Kerberos KDC hands out tickets so users can prove who they are without sending passwords around. Port 389 is LDAP and 443 is HTTPS.

Huh, didn't know that: RFC 4120 says alternate ports may be used when running multiple KDCs.

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References

Answer: Port 88. RFC 4120 says Kerberos servers should listen on port 88 unless configured otherwise. A Kerberos KDC hands out tickets so users can prove who they are without sending passwords around. Port 389 is LDAP and 443 is HTTPS.

  1. IETF RFC 4120, The Kerberos Network Authentication Service (V5) www.rfc-editor.org/rfc/rfc4120
    MUST accept UDP requests and SHOULD listen for them on port 88 (decimal)
    Checked 2026-10-10.

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