Question 883 of 2,152

Network Logging and Syslog →mediumMultiple ChoiceObjective-mapped

ACL Denied Traffic: Repeated Access Attempts from Single Source

This 300-410 practice question tests your understanding of network logging and syslog. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

A network engineer runs the following command on Router R6:

R6# show logging | include %SEC-6-IPACCESSLOGP

*Mar  1 00:01:15.123: %SEC-6-IPACCESSLOGP: list ACL_INBOUND denied tcp 10.0.0.100(12345) -> 192.168.1.1(80), 1 packet
*Mar  1 00:01:20.456: %SEC-6-IPACCESSLOGP: list ACL_INBOUND denied tcp 10.0.0.100(12346) -> 192.168.1.1(80), 1 packet
*Mar  1 00:01:25.789: %SEC-6-IPACCESSLOGP: list ACL_INBOUND denied tcp 10.0.0.100(12347) -> 192.168.1.1(80), 1 packet
*Mar  1 00:01:30.012: %SEC-6-IPACCESSLOGP: list ACL_INBOUND denied tcp 10.0.0.100(12348) -> 192.168.1.1(80), 1 packet

Based on this output, what is the most likely problem?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The ACL ACL_INBOUND is permitting traffic from 10.0.0.100 to 192.168.1.1 on port 80.
Why wrong: The log shows denied packets, so the ACL is blocking, not permitting.
B
A host at 10.0.0.100 is attempting to access a web server at 192.168.1.1 and is being blocked by the ACL.
The log messages clearly indicate that packets from 10.0.0.100 to 192.168.1.1 port 80 are being denied by ACL ACL_INBOUND.
C
The router is experiencing a DoS attack from 192.168.1.1.
Why wrong: The source is 10.0.0.100, not 192.168.1.1.
D
The ACL ACL_INBOUND is not configured on any interface.
Why wrong: If it were not configured, no log messages would be generated.

Full breakdown with real-world context →

Quick Answer

The answer is that a host at 10.0.0.100 is repeatedly attempting to access the web server at 192.168.1.1 and being blocked by ACL ACL_INBOUND. This is correct because the log output shows a clear pattern of denied TCP packets from a single source IP, each with an incrementing source port, targeting the same destination IP and port 80—classic evidence of ACL denied traffic analysis where a host is trying to establish HTTP connections but is stopped by the inbound access list. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your ability to interpret syslog messages for ACL hits and distinguish between a legitimate misconfiguration and a potential reconnaissance attempt, such as a port scan. A common trap is misreading the incrementing source ports as a random attack when it could simply be a client retrying a blocked web request. Memory tip: “Same destination, climbing source ports—think blocked client, not random source.”

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

✓

A host at 10.0.0.100 is attempting to access a web server at 192.168.1.1 and is being blocked by the ACL.

The output shows repeated denied packets from source 10.0.0.100 to destination 192.168.1.1 on port 80 (HTTP). This indicates that a host at 10.0.0.100 is trying to access a web server at 192.168.1.1 but is being blocked by ACL ACL_INBOUND. The pattern suggests a possible scan or attack, or a legitimate access that is being denied due to misconfiguration.

Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

Answer analysis

Option-by-option breakdown

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

✗
The ACL ACL_INBOUND is permitting traffic from 10.0.0.100 to 192.168.1.1 on port 80.
Why it's wrong here
The log shows denied packets, so the ACL is blocking, not permitting.
✓
A host at 10.0.0.100 is attempting to access a web server at 192.168.1.1 and is being blocked by the ACL.
Why this is correct
The log messages clearly indicate that packets from 10.0.0.100 to 192.168.1.1 port 80 are being denied by ACL ACL_INBOUND.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The router is experiencing a DoS attack from 192.168.1.1.
Why it's wrong here
The source is 10.0.0.100, not 192.168.1.1.
✗
The ACL ACL_INBOUND is not configured on any interface.
Why it's wrong here
If it were not configured, no log messages would be generated.

Common exam traps

Common exam trap: ACLs stop at the first match

ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.

Trap categories for this question

Command / output trap
The log shows denied packets, so the ACL is blocking, not permitting.

Detailed technical explanation

How to think about this question

ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.

KKey Concepts to Remember

Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.

TExam Day Tips

Check inbound versus outbound direction.
Read the ACL from top to bottom.
Look for a broader permit or deny above the intended line.

Key takeaway

ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

Real-world example

How this comes up in practice

A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

Visual reference

What to study next

Got this wrong? Here's your next step.

Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 300-410 ACL questions on filtering logic and placement.

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FAQ

Questions learners often ask

What does this 300-410 question test?

Network Logging and Syslog — This question tests Network Logging and Syslog — Standard ACLs match source addresses..

What is the correct answer to this question?

The correct answer is: A host at 10.0.0.100 is attempting to access a web server at 192.168.1.1 and is being blocked by the ACL. — The output shows repeated denied packets from source 10.0.0.100 to destination 192.168.1.1 on port 80 (HTTP). This indicates that a host at 10.0.0.100 is trying to access a web server at 192.168.1.1 but is being blocked by ACL ACL_INBOUND. The pattern suggests a possible scan or attack, or a legitimate access that is being denied due to misconfiguration.

What should I do if I get this 300-410 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Standard ACLs match source addresses.

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