- A
The next-hop 10.10.10.2 is not reachable, and PBR drops packets when no route to the next-hop exists. Configure a fallback route or use 'set ip default next-hop'.
PBR drops packets if the set next-hop is not reachable. Using 'set ip default next-hop' allows PBR to use the routing table as a fallback if the next-hop is unreachable.
- B
The ACL in the route-map is incorrectly denying traffic from 172.16.1.0/24, causing PBR to not match the traffic.
Why wrong: The debug output shows PBR is matching the traffic but cannot find a route to the next-hop, so ACL matching is not the issue.
- C
The interface where PBR is applied is in a different VRF, causing the next-hop to be unreachable.
Why wrong: If the interface were in a different VRF, the PBR configuration would need to be VRF-aware. However, the debug output does not indicate a VRF mismatch, and the next-hop is simply not reachable.
- D
The next-hop 10.10.10.2 is reachable but the route-map has a 'match ip address' that is too specific, excluding some traffic.
Why wrong: The debug output clearly states 'no route to next-hop', indicating the next-hop itself is not reachable, not that traffic is being excluded.
Quick Answer
The answer is that PBR drops traffic when the next-hop is not reachable due to a missing route, which is the root cause of the dropped packets from subnet 172.16.1.0/24. Policy-based routing requires the specified next-hop to be present in the routing table; if no route to that next-hop exists, PBR has no valid path and silently discards the packet. This is a critical concept tested on the Cisco CCNP ENARSI 300-410 exam, often appearing in troubleshooting scenarios where a routing change removes the route to the next-hop, causing unexpected drops even though the route-map and policy are correctly applied. A common trap is assuming PBR will fall back to the regular routing table—it does not unless you explicitly configure a fallback using `set ip default next-hop` or a default route. Remember the memory tip: "PBR needs a path—no route means no route, packet gets the boot."
300-410 Policy-Based Routing (PBR) Practice Question
This 300-410 practice question tests your understanding of policy-based routing (pbr). 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 multi-router network uses PBR to steer traffic from subnet 172.16.1.0/24 through a WAN link (next-hop 10.10.10.2). After a routing change, traffic from this subnet is being dropped. Router R1 shows: 'show route-map' indicates the route-map is applied, 'show ip policy' shows the policy on the interface, but 'debug ip policy' shows 'PBR: no route to next-hop 10.10.10.2'. What is the root cause?
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 next-hop 10.10.10.2 is not reachable, and PBR drops packets when no route to the next-hop exists. Configure a fallback route or use 'set ip default next-hop'.
PBR requires the next-hop to be reachable via a route in the routing table. If the next-hop is not reachable (e.g., due to a routing change or a missing route), PBR will drop the packet unless a fallback is configured. In this case, the next-hop 10.10.10.2 is not reachable, so PBR drops the traffic. The solution is to either ensure the next-hop is reachable or configure a default route or fallback action.
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 next-hop 10.10.10.2 is not reachable, and PBR drops packets when no route to the next-hop exists. Configure a fallback route or use 'set ip default next-hop'.
Why this is correct
PBR drops packets if the set next-hop is not reachable. Using 'set ip default next-hop' allows PBR to use the routing table as a fallback if the next-hop is unreachable.
Related concept
CIDR notation defines the prefix length.
- ✗
The ACL in the route-map is incorrectly denying traffic from 172.16.1.0/24, causing PBR to not match the traffic.
Why it's wrong here
The debug output shows PBR is matching the traffic but cannot find a route to the next-hop, so ACL matching is not the issue.
- ✗
The interface where PBR is applied is in a different VRF, causing the next-hop to be unreachable.
Why it's wrong here
If the interface were in a different VRF, the PBR configuration would need to be VRF-aware. However, the debug output does not indicate a VRF mismatch, and the next-hop is simply not reachable.
- ✗
The next-hop 10.10.10.2 is reachable but the route-map has a 'match ip address' that is too specific, excluding some traffic.
Why it's wrong here
The debug output clearly states 'no route to next-hop', indicating the next-hop itself is not reachable, not that traffic is being excluded.
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
Command / output trap
The debug output shows PBR is matching the traffic but cannot find a route to the next-hop, so ACL matching is not the issue.
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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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) — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The next-hop 10.10.10.2 is not reachable, and PBR drops packets when no route to the next-hop exists. Configure a fallback route or use 'set ip default next-hop'. — PBR requires the next-hop to be reachable via a route in the routing table. If the next-hop is not reachable (e.g., due to a routing change or a missing route), PBR will drop the packet unless a fallback is configured. In this case, the next-hop 10.10.10.2 is not reachable, so PBR drops the traffic. The solution is to either ensure the next-hop is reachable or configure a default route or fallback action.
What should I do if I get this 300-410 question wrong?
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Last reviewed: Jun 18, 2026
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