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Zorluk: ZorCommon Ports and Protocols

A network security administrator is troubleshooting authentication failures for remote client devices connecting to internal corporate resources over a VPN. While directory browsing and LDAP user lookups function normally, domain authentication requests to the Key Distribution Center (KDC) fail whenever kerberos ticket sizes exceed the standard maximum transmission unit (MTU) or fall back to connection-oriented transport. Inspection of the perimeter firewall logs shows blocked traffic destined for the domain controller. Which port and transport protocol combination must be permitted on the firewall to allow complete Kerberos authentication traffic?

  1. TCP and UDP port 88Cevap
  2. B
    UDP port 88 only
  3. C
    TCP port 389
  4. D
    TCP port 445

Cevap

Permitting TCP and UDP port 88 on the firewall is required for full Kerberos authentication functionality.
Kerberos authentication services (KDC) operate on port 88 using both TCP and UDP protocols. UDP port 88 handles standard small authentication requests, while TCP port 88 is required when ticket payloads exceed buffer/MTU sizes or require connection-oriented delivery.

Adım Adım Çözüm

1
Identify the service protocol responsible for ticket-based domain authentication.
The service is Kerberos, managed by the Key Distribution Center (KDC) on domain controllers.
Kerberos is the primary authentication protocol used in enterprise Active Directory domains.
2
Determine the standard port assignment for Kerberos.
Kerberos utilizes standard port 88.
IANA assigns port 88 to the Kerberos authentication system.
3
Evaluate transport layer requirements for Kerberos.
Kerberos uses UDP port 88 by default for lightweight ticket requests, but automatically falls back to TCP port 88 when authentication tickets exceed packet size thresholds or when connection reliability is required.
Firewalls blocking TCP port 88 cause subtle authentication failures when PAC (Privilege Attribute Certificate) data enlarges Kerberos tickets beyond MTU limits.

Anahtar Kavram

Kerberos Port and Transport Protocol Requirements
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Konular

Common Ports and Protocols

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