- A
Traffic that should be policy-routed follows the routing table instead.
This indicates PBR is not matching the traffic or not applied correctly.
- B
High CPU usage on the router when processing PBR traffic.
PBR can cause high CPU if process-switched, especially with large ACLs.
- C
The 'show ip policy' command shows the route-map applied to the interface.
Why wrong: This is a verification command, not a symptom of failure; it confirms PBR is configured.
- D
Packets are dropped when the 'set interface' specifies a down interface.
This is a known behavior: if the interface is down, the packet is dropped unless a fallback next-hop is set.
- E
The routing table is updated with new routes from PBR.
Why wrong: PBR does not modify the routing table; it only affects forwarding decisions.
Quick Answer
The answer is that packets are dropped when the 'set interface' specifies a down interface, traffic follows the routing table instead of the route-map, and high CPU usage occurs due to process-switched PBR with large ACLs. When a 'set interface' points to a down link, the router cannot forward the packet via PBR and drops it, as there is no fallback to the routing table for that specific action. This symptom directly indicates PBR failure because the policy cannot complete its forwarding instruction. On the Cisco CCNP ENARSI 300-410 exam, this topic tests your ability to diagnose PBR misconfigurations versus normal routing behavior; a common trap is confusing the 'show ip policy' command output, which only confirms PBR is applied, not that it is working. Remember that PBR is process-switched by default, so large ACLs can spike CPU usage—a key performance symptom. Memory tip: "Down interface drops, routing table robs, CPU climbs with big ACL jobs."
300-410 Policy-Based Routing (PBR) Practice Question
This 300-410 practice question tests your understanding of policy-based routing (pbr). 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.
Which THREE symptoms indicate that Policy-Based Routing (PBR) is not working as expected? (Choose THREE.)
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
Traffic that should be policy-routed follows the routing table instead.
If traffic that should be policy-routed follows the routing table instead, PBR may not be applied or the route-map may not match. High CPU usage can occur if PBR is process-switched and ACLs are large. If the 'set interface' specifies a down interface, packets are dropped. The 'show ip policy' command shows PBR application, not a symptom of failure. PBR does not affect routing table updates. A mismatch in ACLs can cause unintended forwarding.
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.
- ✓
Traffic that should be policy-routed follows the routing table instead.
Why this is correct
This indicates PBR is not matching the traffic or not applied correctly.
Related concept
Standard ACLs match source addresses.
- ✓
High CPU usage on the router when processing PBR traffic.
Why this is correct
PBR can cause high CPU if process-switched, especially with large ACLs.
Related concept
Standard ACLs match source addresses.
- ✗
The 'show ip policy' command shows the route-map applied to the interface.
Why it's wrong here
This is a verification command, not a symptom of failure; it confirms PBR is configured.
- ✓
Packets are dropped when the 'set interface' specifies a down interface.
Why this is correct
This is a known behavior: if the interface is down, the packet is dropped unless a fallback next-hop is set.
Related concept
Standard ACLs match source addresses.
- ✗
The routing table is updated with new routes from PBR.
Why it's wrong here
PBR does not modify the routing table; it only affects forwarding decisions.
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
This is a verification command, not a symptom of failure; it confirms PBR is configured.
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.
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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Policy-Based Routing (PBR) — study guide chapter
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FAQ
Questions learners often ask
What does this 300-410 question test?
Policy-Based Routing (PBR) — This question tests Policy-Based Routing (PBR) — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Traffic that should be policy-routed follows the routing table instead. — If traffic that should be policy-routed follows the routing table instead, PBR may not be applied or the route-map may not match. High CPU usage can occur if PBR is process-switched and ACLs are large. If the 'set interface' specifies a down interface, packets are dropped. The 'show ip policy' command shows PBR application, not a symptom of failure. PBR does not affect routing table updates. A mismatch in ACLs can cause unintended forwarding.
What should I do if I get this 300-410 question wrong?
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.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Last reviewed: Jun 18, 2026
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