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GSLC · Question #65

You work as a Network Administrator for NetPerfect Inc. You have implemented a firewall on the company's network. You want to ensure that outside users cannot access the internal FTP servers on the…

The correct answer is D. Block the TCP ports 20 and 21 on the firewall. FTP uses TCP ports 20 (data transfer) and 21 (control/command). Blocking both on the firewall prevents outside users from establishing FTP sessions to internal servers.

Security Architecture & Engineering

Question

You work as a Network Administrator for NetPerfect Inc. You have implemented a firewall on the company's network. You want to ensure that outside users cannot access the internal FTP servers on the network. What will you do to accomplish the task?

Options

  • ABlock the TCP port 443 on the firewall.
  • BBlock the UDP port 1701 and TCP port 1723 on the firewall.
  • CBlock the TCP port 80 on the firewall.
  • DBlock the TCP ports 20 and 21 on the firewall.

How the community answered

(33 responses)
  • A
    6% (2)
  • B
    3% (1)
  • C
    3% (1)
  • D
    88% (29)

Why each option

FTP uses TCP ports 20 (data transfer) and 21 (control/command). Blocking both on the firewall prevents outside users from establishing FTP sessions to internal servers.

ABlock the TCP port 443 on the firewall.

TCP port 443 is used for HTTPS (SSL/TLS-encrypted web traffic), not FTP, so blocking it would only affect secure web browsing.

BBlock the UDP port 1701 and TCP port 1723 on the firewall.

UDP port 1701 and TCP port 1723 are used by L2TP and PPTP VPN protocols respectively, not FTP.

CBlock the TCP port 80 on the firewall.

TCP port 80 is used for HTTP (standard web traffic), not FTP, so blocking it would only affect unencrypted web browsing.

DBlock the TCP ports 20 and 21 on the firewall.Correct

FTP relies on two TCP ports - port 21 for the control connection where commands are issued and port 20 for the active-mode data connection where file transfers occur. Blocking both ensures neither the command channel nor the data channel can be established from outside the network, fully preventing FTP access to internal servers.

Concept tested: Firewall port blocking for FTP protocol

Source: https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml

Topics

#firewall rules#FTP#port blocking#network access control

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