Question 1,363 of 2,152

Policy-Based Routing (PBR) →hardMultiple ChoiceObjective-mapped

Quick Answer

The most likely cause is that ACL 140 contains a deny statement for 172.16.2.0/24 placed before the permit statement for the broader 172.16.0.0/16 range. This is because Policy-Based Routing (PBR) processes route-map entries sequentially, and when the ACL is evaluated, the first matching entry determines the action—so a preceding deny for the specific subnet will block that traffic from being matched, even though a later permit covers the entire /16. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how PBR interacts with ACL order and route-map sequence numbers, often appearing as a trap where engineers assume a broad permit alone guarantees all subnets are matched. A common memory tip is “first match wins in PBR—check both ACL line order and route-map sequence order when you see subnet-specific failure.”

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.

A network engineer is troubleshooting PBR on a Cisco router where traffic from subnet 172.16.0.0/16 should be forwarded to next-hop 10.10.10.2. The route map 'PBR-172' is configured with 'match ip address 140' and 'set ip next-hop 10.10.10.2'. The engineer applies the route map to interface GigabitEthernet0/0. The engineer notices that PBR works for traffic from 172.16.1.0/24 but not for traffic from 172.16.2.0/24. The engineer checks the ACL 140 and confirms it includes the entire 172.16.0.0/16 subnet. What is the most likely cause?

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.

Question 1hardmultiple choice

Study the full ACL explanation →

A
The route map has a sequence that matches 172.16.1.0/24 with a permit, and a later sequence that denies 172.16.2.0/24.
Correct because route maps are processed in sequence order; a later deny statement can override an earlier permit.
B
The ACL 140 has a deny statement for 172.16.2.0/24 before the permit statement.
Correct because ACLs are processed top-down; a deny statement before the permit will cause the traffic to be denied and not matched by the route map.
C
The next-hop 10.10.10.2 is not reachable from the 172.16.2.0/24 subnet.
Why wrong: Incorrect because reachability is not subnet-specific; if the next-hop is reachable, it is reachable from all subnets.
D
The 'ip policy route-map' command is applied to a subinterface that only receives traffic from 172.16.1.0/24.
Why wrong: Incorrect because the scenario states the route map is applied to interface GigabitEthernet0/0, not a subinterface.

Full breakdown with real-world context →

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

✓

The route map has a sequence that matches 172.16.1.0/24 with a permit, and a later sequence that denies 172.16.2.0/24.

If PBR works for one subnet but not another within the same ACL, it could be due to the route map having multiple sequence statements with different match conditions, or the ACL having specific permit statements that are ordered incorrectly. However, a common cause is that the route map has a sequence with a more specific match that matches 172.16.1.0/24 and a subsequent sequence that denies 172.16.2.0/24. The engineer should check the route map sequence numbers and the ACL order.

Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

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 route map has a sequence that matches 172.16.1.0/24 with a permit, and a later sequence that denies 172.16.2.0/24.
Why this is correct
Correct because route maps are processed in sequence order; a later deny statement can override an earlier permit.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
✓
The ACL 140 has a deny statement for 172.16.2.0/24 before the permit statement.
Why this is correct
Correct because ACLs are processed top-down; a deny statement before the permit will cause the traffic to be denied and not matched by the route map.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
✗
The next-hop 10.10.10.2 is not reachable from the 172.16.2.0/24 subnet.
Why it's wrong here
Incorrect because reachability is not subnet-specific; if the next-hop is reachable, it is reachable from all subnets.
✗
The 'ip policy route-map' command is applied to a subinterface that only receives traffic from 172.16.1.0/24.
Why it's wrong here
Incorrect because the scenario states the route map is applied to interface GigabitEthernet0/0, not a subinterface.

Common exam traps

Common exam trap: usable hosts are not the same as total addresses

Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.

Trap categories for this question

Scenario analysis trap
Incorrect because the scenario states the route map is applied to interface GigabitEthernet0/0, not a subinterface.

Detailed technical explanation

How to think about this question

Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.

KKey Concepts to Remember

CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.

TExam Day Tips

Write the block size before choosing the subnet.
Check whether the question asks for hosts, subnets or a specific address range.
Do not confuse /24, /25, /26 and /27 host counts.

Key takeaway

Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

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 block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 300-410 subnetting questions on CIDR, address ranges, and subnet selection.

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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) — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: The route map has a sequence that matches 172.16.1.0/24 with a permit, and a later sequence that denies 172.16.2.0/24. — If PBR works for one subnet but not another within the same ACL, it could be due to the route map having multiple sequence statements with different match conditions, or the ACL having specific permit statements that are ordered incorrectly. However, a common cause is that the route map has a sequence with a more specific match that matches 172.16.1.0/24 and a subsequent sequence that denies 172.16.2.0/24. The engineer should check the route map sequence numbers and the ACL order.

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?

CIDR notation defines the prefix length.

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