The answer is that the ACL in the route-map is configured to match only TCP traffic, so UDP packets are not policy-routed. Policy-Based Routing (PBR) processes all IP traffic by default, but the route-map relies on an Access Control List (ACL) to define which packets are matched; if that ACL specifies the protocol as "tcp," it will only match TCP segments, leaving UDP datagrams to be forwarded normally without the policy-route. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of PBR ACL protocol matching—a common trap is assuming PBR inherently applies to all traffic, when in fact the ACL’s protocol field is the gatekeeper. Remember that to policy-route both TCP and UDP, the ACL must use "ip" as the protocol, not "tcp" or "udp." A quick memory tip: "PBR picks packets by protocol—if you only say TCP, UDP gets the free pass."
300-410 Policy-Based Routing (PBR) Practice Question
This 300-410 practice question tests your understanding of policy-based routing (pbr). This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 router is configured with PBR using a route-map that sets the next-hop to 10.0.0.2 for traffic from subnet 192.168.1.0/24. The route-map is applied inbound on interface GigabitEthernet0/0. The engineer also configures 'ip policy route-map' on the same interface. The engineer notices that PBR is working for TCP traffic but not for UDP traffic from the same 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The ACL in the route-map is configured to match only TCP traffic, so UDP packets are not policy-routed.
PBR processes all IP traffic regardless of protocol, but if the ACL in the route-map uses 'tcp' as the protocol, it will only match TCP packets. The engineer likely configured the ACL to match only TCP, inadvertently excluding UDP. The ACL should use 'ip' to match all protocols.
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 ACL in the route-map is configured to match only TCP traffic, so UDP packets are not policy-routed.
Why this is correct
ACL protocol matching is specific; using 'tcp' excludes UDP.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The next-hop 10.0.0.2 does not have a route for UDP traffic.
Why it's wrong here
Routing is based on destination IP, not protocol.
✗
The route-map is missing a 'set ip next-hop' command for UDP.
Why it's wrong here
The set command applies to all matched traffic; the issue is in the match criteria.
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 set command applies to all matched traffic; the issue is in the match criteria.
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: The ACL in the route-map is configured to match only TCP traffic, so UDP packets are not policy-routed. — PBR processes all IP traffic regardless of protocol, but if the ACL in the route-map uses 'tcp' as the protocol, it will only match TCP packets. The engineer likely configured the ACL to match only TCP, inadvertently excluding UDP. The ACL should use 'ip' to match all protocols.
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.
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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