mediumMultiple Choice
Firewall Default Deny: Rule Order Placement
A security administrator is configuring a stateful firewall to allow HTTP traffic from the internet to a web server. The firewall uses a default-deny policy. What is the correct rule placement?
Quick Answer
The correct rule placement is to put the allow rule before the deny all rule. This is because a stateful firewall with a default-deny policy processes rules sequentially from top to bottom, so the explicit permit for HTTP traffic (TCP port 80) must be evaluated first to match and allow the desired packets before the catch-all deny rule drops everything else. On the CISSP exam, this concept tests your understanding of firewall rule ordering and the principle of least privilege, often appearing in questions about access control lists or network security architecture. A common trap is assuming a default-deny policy automatically allows known traffic, but the deny all rule will block it if placed first, making the allow rule unreachable. Remember the memory tip: “First allow, then deny—or your traffic will say goodbye.”
⚠ Common exam trap
ISC2 often tests the misconception that a default-deny policy automatically allows traffic if a permit rule exists anywhere in the ACL, but in reality, rule order determines which rule is applied first, and a deny all placed before the permit will block all traffic.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Place the allow rule before the deny all rule
In a stateful firewall with a default-deny policy, rules are processed in sequential order from top to bottom. Placing the allow rule before the deny all rule ensures that HTTP traffic (TCP port 80) is explicitly permitted before the catch-all deny rule drops all unmatched packets. If the deny all rule were placed first, all traffic would be dropped, including the intended HTTP traffic, making the allow rule unreachable.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Place the allow rule after the deny all rule
Why it's wrong here
Rules are evaluated top-down, so an allow placed after deny-all is never reached and HTTP remains blocked. It is tempting because appending the permit seems tidy, and would be correct if the deny rule sat at the bottom as an explicit final catch-all, but here it precedes and shadows the permit.
- ✗
Use a stateless firewall instead
Why it's wrong here
Replacing the stateful firewall with a stateless one discards the connection-tracking table that lets return HTTP traffic through without a separate inbound rule, so replies to outbound sessions would be dropped under default-deny. Stateless filtering suits scenarios demanding fixed, direction-independent packet rules, such as simple ACLs on routers.
- ✗
Use an implicit deny rule
Why it's wrong here
An implicit deny is the firewall's built-in final catch-all, not a rule the administrator places; adding it explicitly does nothing to permit HTTP. It is tempting because default-deny policies rely on it, and it would be correct as the trailing behaviour after all explicit allow rules, but it cannot authorise inbound port 80.
- ✓
Place the allow rule before the deny all rule
Why this is correct
With default-deny, the firewall evaluates rules top-down and stops at the first match. The allow rule for HTTP must precede the deny-all rule, otherwise the deny rule matches first and blocks the permitted web traffic.
Visual reference
Go deeper
Related to this question
Key term
Security
Security in IT is the practice of protecting systems, networks, and data from unauthorized access, damage, or theft.
Key term
Firewall
A firewall is a network security system that monitors and controls incoming and outgoing traffic based on predetermined security rules to protect trusted internal networks from untrusted external networks.
About these practice questions
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Same concept, more angles
1 more way this is tested on CISSP
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Refer to the exhibit. The firewall rules above are applied to the outside interface. A penetration tester from the internet attempts to establish a connection to 192.168.1.10 on TCP port 8080. What will happen?
medium- A.The connection is permitted only if the tester uses a VPN
- B.The connection is permitted
- C.The connection is denied because the destination is not reachable
- ✓ D.The connection is denied because the port is not explicitly allowed
Why D: The stem begins with 'Refer to the exhibit', but no exhibit or table of firewall rules is provided. Furthermore, the question states that a tester 'from the internet attempts to establish a connection to 192.168.1.10'. Because 192.168.1.10 is a private RFC 1918 IP address, it is non-routable over the public internet. Without destination NAT (DNAT) or a VPN (which Option A mentions but is marked wrong), a tester on the internet cannot target this IP directly. Thus, the connection would fail due to routing before even evaluating firewall port rules.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CISSP practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CISSP exam.