A network security administrator is transitioning a segment from a stateful firewall to a … — CompTIA Network+

A network security administrator is transitioning a segment from a stateful firewall to a router utilizing stateless extended IPv4 Access Control Lists (ACLs). The administrator configures an inbound ACL on the interface connecting internal monitoring workstations ( $172.16.10.0/24$ ) to allow diagnostic queries to a remote Syslog server ( $10.20.30.50$ ) using UDP port $514$ . After applying the ACL, technicians report that while outbound query packets are sent successfully, return diagnostic responses from the Syslog server are blocked. Which statement accurately explains why this communication failure occurs?

Stateless ACLs inspect packets individually without maintaining session state tables, meaning return traffic from the Syslog server is blocked unless explicitly permitted by a return ACL rule.Answer
B
The inbound ACL rule allows the request, but the implicit deny at the end of the ACL automatically drops UDP packets because they lack an ESTABLISHED flag.
C
Extended IPv4 ACLs operate strictly at Layer 2 of the OSI model, making them incapable of inspecting Layer 4 transport protocol fields like UDP port numbers.
D
The configured ACL rule specifies port 514, but standard Syslog services operate exclusively over TCP port 22, resulting in a port mismatch that drops the traffic.

Answer

Stateless ACLs inspect packets individually without maintaining session state tables, meaning return traffic from the Syslog server is blocked unless explicitly permitted by a return ACL rule.

Stateful firewalls maintain connection tracking tables that dynamically permit return traffic associated with established sessions. In contrast, stateless router ACLs evaluate every packet independently. When replacing a stateful firewall with stateless ACLs, an explicit rule must be created to allow response packets traveling in the reverse direction, as they will otherwise be blocked by the implicit deny statement.

Step-by-Step Solution

Differentiate between stateful firewall operation and stateless ACL processing.

Stateful firewalls track connection states (e.g., TCP handshakes, active UDP pseudo-sessions) in a state table, automatically allowing reverse return flows for permitted outbound connections. Stateless ACLs process every packet independently against configured rules without context of prior packets.

Understanding the fundamental operational difference between stateful firewalls and stateless router ACLs is essential for network access troubleshooting.

Analyze the directional packet flow for UDP communication.

Outbound packet flow: Source

172.16.10.0/24 \rightarrow

Destination

10.20.30.50:514

(Permitted by inbound ACL).
Return packet flow: Source

10.20.30.50:514 \rightarrow

Destination

172.16.10.0/24

(No explicit permit rule; hit by implicit deny).

Because UDP is connectionless and the ACL is stateless, return packets are evaluated independently against the interface rules.

Identify the required configuration modification to restore bi-directional communication.

An explicit return rule must be configured on the appropriate interface to permit traffic originating from

10.20.30.50

with source UDP port

514

back to the

172.16.10.0/24

subnet.

Without a state table or an explicit return permit rule, return packets encounter the implicit deny all statement at the end of the stateless ACL.

Key Concept

Stateful Firewalls vs. Stateless Access Control Lists (ACLs)

Estimated Time:2m 0s

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