Question 1,177 of 2,152

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

Quick Answer

The answer is that the route-map is missing the `set ip next-hop verify-availability` command, which causes PBR to forward traffic to an unreachable next-hop. Policy-based routing (PBR) uses a route-map to match specific traffic and then override the routing table by setting a next-hop, but without the verify-availability keyword, the router will blindly send packets to the configured next-hop even if that address is not reachable via any routing protocol or connected interface. In this scenario, next-hop 10.2.2.2 is unreachable, so PBR black-holes the matched traffic from subnet 10.1.1.0/24, while unmatched traffic is correctly load-balanced to 10.3.3.3. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of how PBR interacts with reachability checks; a common trap is assuming PBR automatically validates next-hop reachability. Remember the mnemonic: “PBR without verify is a blind driver—it will drive off a cliff if the bridge is out.”

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 large enterprise network is experiencing intermittent reachability from a specific subnet (10.1.1.0/24) to a critical server (192.168.10.10). Router R1 has PBR configured to forward traffic from 10.1.1.0/24 to next-hop 10.2.2.2, but traffic is also being load-balanced via the routing table to 10.3.3.3. Router R2 shows: 'show ip route 192.168.10.10' returns a route via 10.4.4.4, but 'show ip policy' on R1 shows the route-map is applied. What is the root cause?

Question 1hardmultiple choice

Review the full subnetting walkthrough →

A
The route-map is missing the 'set ip next-hop verify-availability' command, causing PBR to forward traffic to an unreachable next-hop.
Without 'verify-availability', PBR does not check if the next-hop is reachable. Adding this command ensures PBR only uses the next-hop if it is reachable, falling back to the routing table otherwise.
B
The ACL in the route-map is incorrectly matching traffic from 10.1.1.0/24, causing PBR to be applied to the wrong traffic.
Why wrong: The ACL is correctly matching the subnet, as evidenced by the symptom. The issue is with next-hop reachability, not ACL matching.
C
The routing table on R1 has a higher administrative distance for the route to 192.168.10.10 via 10.3.3.3, causing PBR to be ignored.
Why wrong: PBR overrides the routing table for matched traffic, regardless of administrative distance. The routing table only applies if PBR is not configured or if the route-map does not match.
D
The next-hop 10.2.2.2 is reachable but the path is congested, causing intermittent packet drops.
Why wrong: The symptom is due to unreachability, not congestion. The 'verify-availability' command would still be needed to detect the unreachability.

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 is missing the 'set ip next-hop verify-availability' command, causing PBR to forward traffic to an unreachable next-hop.

PBR uses a route-map to match traffic and set next-hop. If the route-map does not have a 'set ip next-hop verify-availability' command, PBR will forward traffic to the next-hop even if it is not reachable. In this scenario, the next-hop 10.2.2.2 is not reachable, but PBR still forwards traffic to it, causing intermittent reachability. The routing table load-balancing to 10.3.3.3 works, but PBR overrides it for matched traffic.

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 is missing the 'set ip next-hop verify-availability' command, causing PBR to forward traffic to an unreachable next-hop.
Why this is correct
Without 'verify-availability', PBR does not check if the next-hop is reachable. Adding this command ensures PBR only uses the next-hop if it is reachable, falling back to the routing table otherwise.
Related concept
CIDR notation defines the prefix length.
✗
The ACL in the route-map is incorrectly matching traffic from 10.1.1.0/24, causing PBR to be applied to the wrong traffic.
Why it's wrong here
The ACL is correctly matching the subnet, as evidenced by the symptom. The issue is with next-hop reachability, not ACL matching.
✗
The routing table on R1 has a higher administrative distance for the route to 192.168.10.10 via 10.3.3.3, causing PBR to be ignored.
Why it's wrong here
PBR overrides the routing table for matched traffic, regardless of administrative distance. The routing table only applies if PBR is not configured or if the route-map does not match.
✗
The next-hop 10.2.2.2 is reachable but the path is congested, causing intermittent packet drops.
Why it's wrong here
The symptom is due to unreachability, not congestion. The 'verify-availability' command would still be needed to detect the unreachability.

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 symptom is due to unreachability, not congestion. The 'verify-availability' command would still be needed to detect the unreachability.

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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.

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 is missing the 'set ip next-hop verify-availability' command, causing PBR to forward traffic to an unreachable next-hop. — PBR uses a route-map to match traffic and set next-hop. If the route-map does not have a 'set ip next-hop verify-availability' command, PBR will forward traffic to the next-hop even if it is not reachable. In this scenario, the next-hop 10.2.2.2 is not reachable, but PBR still forwards traffic to it, causing intermittent reachability. The routing table load-balancing to 10.3.3.3 works, but PBR overrides it for matched traffic.

What should I do if I get this 300-410 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

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