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Question

Difficulty: HardCommon Ports and Protocols

A network security engineer is defining stateful perimeter firewall rules to enforce infrastructure security baselines. Match each network protocol and operational scenario to its correct default transport protocol and port number.

  • Kerberos user authentication and ticket granting service requestsTCP/UDP Port 88
  • TACACS+ centralized administrative AAA communication for router managementTCP Port 49
  • IPsec Internet Key Exchange (IKE) Phase 1 tunnel negotiationUDP Port 500
  • Trivial File Transfer Protocol (TFTP) bootstrap image provisioningUDP Port 69

Answer

Kerberos authentication pairs with TCP/UDP Port 88. TACACS+ router administration pairs with TCP Port 49. IPsec IKE tunnel negotiation pairs with UDP Port 500. TFTP bootstrap image provisioning pairs with UDP Port 69.
Matching each network operational service to its exact transport layer port requires recognizing protocol functions: Kerberos utilizes TCP/UDP port 88, TACACS+ utilizes TCP port 49, IPsec IKE utilizes UDP port 500, and TFTP utilizes UDP port 69.

Step-by-Step Solution

1
Identify the primary transport requirements and default ports for directory/authentication services.
Kerberos requires port 88 over both TCP and UDP for domain authentication and key distribution.
Domain controllers listen on port 88 for ticket requests.
2
Differentiate administrative AAA security protocols by transport behavior and port assignments.
TACACS+ uses TCP port 49 for full packet encryption and reliable delivery, unlike RADIUS which uses UDP ports 1812/1813.
Cisco TACACS+ relies on TCP connection-oriented delivery to manage network hardware administration securely.
3
Determine the ISAKMP/IKE control plane port for IPsec VPN negotiation.
Internet Key Exchange (IKE) Phase 1 and Phase 2 negotiations initiate over UDP port 500.
VPN gateways exchange keying material using UDP port 500 prior to encapsulating data.
4
Identify the connectionless boot loading file transfer protocol port.
TFTP listens on UDP port 69 for initial download requests.
TFTP minimizes client memory overhead during network booting by leveraging UDP instead of TCP.

Key Concept

Core Administrative, Authentication, and Infrastructure Service Ports
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Topics

Common Ports and Protocols

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