N10-009 Network Security Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  A) Port forwarding (DNAT) rule

  Why this is correct

  Port forwarding, also known as Destination Network Address Translation (DNAT), is the correct solution because it modifies the destination IP address and port of incoming network packets. When an external client sends traffic to the firewall's public IP address on a specific port, the DNAT rule translates this public address and port to the internal private IP address and port of the target server. This allows the remote employees' traffic, destined for the public IP, to be correctly routed to the internal server within the private network, making the service externally accessible.

• ✗

  B) Allow rule with source any, destination 10.0.0.5, port 443

  Why it's wrong here

  An allow rule with a destination of 10.0.0.5 would permit traffic *if* the packet's destination IP was already 10.0.0.5. However, incoming traffic from the internet is addressed to the firewall's public IP (e.g., 203.0.113.10), not the internal private IP. Without an accompanying address translation mechanism like DNAT, the firewall would simply drop or reject packets whose destination IP does not match an interface or a routing entry, as the internal server's private IP is not directly reachable from the internet.

• ✗

  C) Access control list on the internal interface

  Why it's wrong here

  An Access Control List (ACL) applied to an internal interface primarily governs traffic flow *within* the private network or traffic attempting to *exit* the private network through that interface. While an ACL can filter traffic based on source, destination, and port, it does not perform the crucial function of translating public IP addresses to private ones for incoming external connections. Therefore, an internal ACL cannot enable remote employees to initiate connections to an internal server from the internet.

  When this WOULD be correct

  This option would be correct if the question asked about controlling outbound traffic from the internal network to the internet, such as restricting which internal users can access external web servers on port 443.

• ✗

  D) VPN rule to require remote access VPN

  Why it's wrong here

  A VPN rule would mandate that remote employees establish a Virtual Private Network tunnel to the corporate network before accessing any internal resources. While VPNs provide secure remote access, the question implies a direct internet-based access method for a service, not a requirement for users to connect via a VPN client. Implementing a VPN rule would prevent direct public access to the service and instead force all remote connections through a secure, encrypted tunnel, which is not the stated goal.

  When this WOULD be correct

  A VPN rule would be correct if the scenario required secure, encrypted access to the entire internal network or multiple services, and the organization policy mandated that all remote access must go through a VPN for security compliance.

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.

Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”