Question 410 of 2,152

Network Logging and Syslog →hardMultiple ChoiceObjective-mapped

Troubleshooting Syslog Connectivity Failures on Cisco Routers

This 300-410 practice question tests your understanding of network logging and syslog. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.

An engineer configures syslog logging to a remote server using the 'logging host' command. The engineer notices that syslog messages are not being received on the server, but the router can ping the server successfully. The engineer verifies that the logging level is set to debugging and that the server is configured to receive syslog messages. Which is the most likely explanation?

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
An ACL on the router is blocking UDP port 514 outbound
Correct. If an ACL is applied to the interface that blocks UDP 514, syslog messages will not reach the server.
B
The logging host command requires the 'transport tcp' option to work
Why wrong: Syslog uses UDP by default, and TCP is optional.
C
The syslog server is not configured to accept messages from the router's IP
Why wrong: This is possible but less common; the question states the server is configured.
D
The logging level is set to emergencies only
Why wrong: The engineer set the level to debugging, so this is not the issue.

Full breakdown with real-world context →

Quick Answer

The answer is that an ACL on the router blocking UDP port 514 outbound is the most likely explanation. Syslog messages are transmitted over UDP port 514 by default, and even when the router can ping the server successfully—confirming IP-level reachability—a configured access control list can silently drop the outbound syslog traffic without any error message. This scenario tests your understanding of how Cisco IOS handles syslog generation and the critical distinction between ICMP reachability and UDP port-level filtering, a common trap on the CCNP ENARSI 300-410 exam. Many candidates overlook that a successful ping only verifies Layer 3 connectivity, not that the specific UDP syslog port is permitted. A useful memory tip is to think of syslog as a “UDP-only messenger” that needs a clear path on port 514, so always check both the router’s outbound ACL and any firewall rules on the server side when troubleshooting syslog not received router issues.

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

✓

An ACL on the router is blocking UDP port 514 outbound

A common edge case is that the syslog messages are sent via UDP port 514, but the router may have a firewall or ACL that blocks UDP traffic. Additionally, the 'logging source-interface' command might be configured, but if the source interface is not reachable from the server (e.g., due to routing issues), the server may drop the messages. Another possibility is that the server is listening on a different port or the router is using a different port due to configuration. However, a less obvious issue is that the 'logging monitor' or 'logging buffered' commands can interfere if the logging process is overwhelmed, but the most likely is that the syslog messages are being sent but the server's firewall or the router's own ACL is blocking them.

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.

✓
An ACL on the router is blocking UDP port 514 outbound
Why this is correct
Correct. If an ACL is applied to the interface that blocks UDP 514, syslog messages will not reach the server.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The logging host command requires the 'transport tcp' option to work
Why it's wrong here
Syslog uses UDP by default, and TCP is optional.
✗
The syslog server is not configured to accept messages from the router's IP
Why it's wrong here
This is possible but less common; the question states the server is configured.
✗
The logging level is set to emergencies only
Why it's wrong here
The engineer set the level to debugging, so this is not the issue.

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.

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: An ACL on the router is blocking UDP port 514 outbound — A common edge case is that the syslog messages are sent via UDP port 514, but the router may have a firewall or ACL that blocks UDP traffic. Additionally, the 'logging source-interface' command might be configured, but if the source interface is not reachable from the server (e.g., due to routing issues), the server may drop the messages. Another possibility is that the server is listening on a different port or the router is using a different port due to configuration. However, a less obvious issue is that the 'logging monitor' or 'logging buffered' commands can interfere if the logging process is overwhelmed, but the most likely is that the syslog messages are being sent but the server's firewall or the router's own ACL is blocking them.

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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Same concept, more angles

1 more ways this is tested on 300-410

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. Drag and drop the steps to troubleshoot syslog connectivity failures into the correct order, from first to last.

hard

✓ A.Ping syslog server from router
✓ B.Check syslog server port accessibility
✓ C.Review logging configuration on router
✓ D.Examine ACLs blocking syslog traffic
✓ E.Enable debug ip udp for syslog monitoring

Why A: First, verify reachability to the syslog server using ping. Then, check if the syslog server port (UDP 514) is open. Next, review the logging configuration on the router. After that, examine ACLs that may block syslog traffic. Finally, enable debug ip udp to monitor syslog packet flow.

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