Examkin

Question

Difficulty: EasyFirewalls and Access Control Lists (ACLs)

A network administrator configures an Access Control List (ACL) with explicit permit statements for HTTP and HTTPS traffic on a router interface. However, users report that all other traffic attempting to pass through this interface is blocked, even though no deny statements were explicitly written. Which of the following features accounts for this behavior?

  1. The implicit deny statement automatically appended to the end of the ACLAnswer
  2. B
    The restriction of extended ACLs to OSI Layer 2 frame processing
  3. C
    The automatic redirection of unmatched packets to a Port Address Translation (PAT) overload pool
  4. D
    The automatic conversion of unlisted TCP packets into connectionless UDP datagrams

Answer

The implicit deny statement automatically appended to the end of the ACL accounts for blocking all unspecified traffic.
The correct option correctly identifies the default behavior of Access Control Lists. Every ACL concludes with an invisible implicit deny rule (e.g., 'deny ip any any'). If incoming or outgoing traffic does not match any explicit permit statement, it hits this final rule and is dropped.

Step-by-Step Solution

1
Analyze the configured ACL entries and observe that only HTTP and HTTPS permit rules were created.
Identified that no explicit rules exist for other traffic types (such as ICMP, SSH, or DNS).
ACL entries are processed sequentially from top to bottom until a match is found.
2
Evaluate default router ACL behavior when no rule matches a packet.
Recognize that network ACLs feature a default implicit deny rule at the very bottom of the rule list.
Security best practices enforce default-deny posture to block all non-permitted traffic.

Key Concept

ACL Implicit Deny Rule
Estimated Time:45s
Rate this question

Topics

Firewalls and Access Control Lists (ACLs)

More questions from this topic