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 172.16.1.0/24 should be forwarded to next-hop 10.10.10.2. The route map 'PBR-172' is applied to interface GigabitEthernet0/0. The engineer notices that the PBR policy is not working at all. The engineer checks the route map configuration and sees 'match ip address 110' and 'set ip next-hop 10.10.10.2'. The engineer also checks the ACL 110 and confirms it matches 172.16.1.0/24. The engineer then checks the interface configuration and sees 'ip policy route-map PBR-172' applied. What should the engineer do next to isolate the issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Check if the next-hop 10.10.10.2 is reachable via the routing table.
The engineer should verify that the next-hop 10.10.10.2 is reachable via a directly connected interface or a static route. PBR will not forward traffic to a next-hop that is not in the routing table or not directly connected, and will fall back to the routing table. The engineer can use 'show ip route 10.10.10.2' to check reachability.
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.
✓
Check if the next-hop 10.10.10.2 is reachable via the routing table.
Why this is correct
Correct because PBR requires the next-hop to be reachable; if not, traffic uses the routing table.
Add the 'set ip default next-hop' command to the route map.
Why it's wrong here
Incorrect because 'set ip default next-hop' is used for default routing, not for PBR; it would not fix the issue.
✗
Change the route map to use 'set interface' instead of 'set ip next-hop'.
Why it's wrong here
Incorrect because the issue is likely reachability, not the type of set command.
✗
Apply the route map to the outgoing interface instead of the incoming interface.
Why it's wrong here
Incorrect because PBR must be applied to the incoming interface; applying to outgoing interface would not work.
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
Incorrect because the issue is likely reachability, not the type of set command.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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.
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: Check if the next-hop 10.10.10.2 is reachable via the routing table. — The engineer should verify that the next-hop 10.10.10.2 is reachable via a directly connected interface or a static route. PBR will not forward traffic to a next-hop that is not in the routing table or not directly connected, and will fall back to the routing table. The engineer can use 'show ip route 10.10.10.2' to check reachability.
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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