Blocking External Proxy Bypass of Firewall URL Filtering
Short answer
B Add a firewall ACE that denies outbound access to the unauthorized external proxy server, preventing employees from bypassing URL filtering.
Question
Key Takeaways
The exam tests whether you choose an enforcement-point control—an outbound firewall ACE—over visibility or endpoint-only fixes; the trap is treating URL filtering as sufficient when traffic never reaches the filtered path.
External proxy bypass of firewall URL filtering is mitigated by adding an outbound firewall ACE that blocks employee access to the proxy server. This guide explains why option B is the enforceable control and why monitoring, VPNs, and hosts-file edits fall short.
Common mistake: The most plausible wrong answer is A: setting up a jump box to monitor proxy traffic provides visibility but leaves access open; mitigation requires blocking the external proxy at the firewall with an ACE (B).
Expert Analysis
The bypass path
Firewall URL filtering only inspects traffic that crosses the firewall and matches a known destination. When an employee uses an external proxy, the workstation connects to that proxy—often over TCP 80/443 or an alternate proxy port—so the firewall may see only the proxy address, not the restricted site. The real URL category is never evaluated, which is why the filter appears ineffective.
Why option B is the enforceable fix
Option B is correct: add an ACE to the firewall's outbound ACL that denies internal users access to the unauthorized external proxy, with logging and an exception process. This enforces policy at the network choke point, where all user traffic passes, instead of trusting each computer's configuration. A commenter frames it correctly—an ACE within an ACL blocks outbound traffic to known external proxies, IP addresses, or unauthorized proxy ports, preventing employees from using that path. Identify the proxy by FQDN and resolved addresses when possible, and deny the address or range when only an IP is known.
Adjacent decisions and the flip
If the external proxy were actually a sanctioned corporate egress proxy, the answer would change: allow it and filter at that proxy rather than block it. If the unauthorized proxy rotates IPs and domains, a single static ACE is necessary but not sufficient; add URL-category blocking for proxy avoidance and anonymizers, DNS filtering, and logging. These strengthen B; they do not replace the outbound deny rule.
Why the other options fail
Option A provides visibility, not mitigation—a jump box watching proxy traffic leaves access open. Option C sends users through a VPN, which does not stop them reaching the proxy and may hide traffic further. Option D edits a local hosts file that is per-machine, easily changed, and ineffective if the proxy is reached by IP or another name. Choosing A, C, or D leaves URL filtering advisory, so data-loss and compliance exposure continue.
Official Reference
- https://www.comptia.org/certifications/network
- https://www.comptia.org/training/resources/exam-objectives
These links open the official vendor documentation in a new tab.
Exam Strategy
When a question describes a policy being bypassed, identify the enforcement point and choose the option that denies the bypass path, not one that merely observes it. In firewall questions, translate ACE or ACL into a rule at the choke point; eliminate VPNs, host-file edits, and jump boxes unless the stem asks for visibility or investigation. Watch for wording such as best mitigate—it points to prevention—and remember that URL filtering only works when traffic actually traverses the firewall.
Frequently Asked Questions
Why doesn't URL filtering on the firewall stop an external proxy server?
Would blocking the proxy's IP address in a firewall ACE always be enough?
Why is editing the hosts file a weaker fix than a firewall ACE?
Discussion 1 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 1
-
ERB14 👍 1 Answered BB. Add an ACE (Access Control Entry) to the firewall for the proxy server: Employees are bypassing the company's URL filtering by connecting to an external proxy server. By adding an ACE (a rule within an Access Control List, or ACL) to block outbound traffic to known external proxy servers, IP addresses, or unauthorized proxy ports on the firewall, the organization can effectively prevent employees from accessing them.
Reader comments & corrections
No reader corrections yet — spotted an error or have a note? Share it below.
Related Analysis
Practice All N10-009 Questions
Access 100 questions with complete answers and detailed explanations.
View Full N10-009 Practice Test →