- A
OSPF adjacency is failing due to CoPP dropping Hello packets.
Why wrong: The output shows successful Hello exchange and transition to FULL state.
- B
OSPF adjacency is established successfully, indicating CoPP is not blocking OSPF traffic.
The adjacency reached FULL state, meaning OSPF packets are being processed correctly.
- C
OSPF is experiencing packet loss due to MTU mismatch.
Why wrong: The MTU of 1500 is mentioned, but no errors are indicated.
- D
OSPF is stuck in EXSTART state due to CoPP.
Why wrong: The output shows transition from EXSTART to FULL.
Question 117 of 2,152
Using OSPF Adjacency Debug to Confirm CoPP Is Not Dropping Hello Packets
This 300-410 practice question tests your understanding of control plane policing (copp). 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 runs the following command to troubleshoot a Control Plane Policing (CoPP) issue:
R1# debug ip ospf adj
OSPF adjacency debugging is on R1#
*Mar 1 00:05:23.123: OSPF: Rcv pkt from 10.1.1.2, FastEthernet0/0, area 0.0.0.0, packet type: 1 (Hello) *Mar 1 00:05:23.123: OSPF: 2 Way Communication to 10.1.1.2 on FastEthernet0/0, state 2WAY *Mar 1 00:05:23.124: OSPF: Send immediate hello to nbr 10.1.1.2, src address 10.1.1.1, on FastEthernet0/0 *Mar 1 00:05:23.124: OSPF: Rcv pkt from 10.1.1.2, FastEthernet0/0, area 0.0.0.0, packet type: 2 (DBD) *Mar 1 00:05:23.125: OSPF: Rcv DBD from 10.1.1.2, seq 0x1234, opts 0x2, flag 0x7, mtu 1500 state EXSTART *Mar 1 00:05:23.126: OSPF: Nbr 10.1.1.2 has state FULL
What does this output indicate?
Quick Answer
The correct interpretation is that the OSPF adjacency is fully established, confirming that CoPP is not dropping Hello packets or any other OSPF traffic. This debug output shows the complete adjacency formation process—from receiving a Hello packet and establishing two-way communication, through the Database Description (DBD) exchange, to the FULL state—which proves that Control Plane Policing policies are permitting OSPF packets to reach the router’s control plane. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your ability to correlate debug output with CoPP functionality; a common trap is assuming any debug message indicates a problem, when in fact the progression to FULL state is the definitive sign of success. Remember that CoPP drops would manifest as missing Hello packets or a stuck state like INIT or EXSTART, not a clean transition to FULL. A useful memory tip: “FULL state means CoPP is not null”—if you see FULL, CoPP is allowing the flow.
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
✓
OSPF adjacency is established successfully, indicating CoPP is not blocking OSPF traffic.
The debug output shows the OSPF adjacency progressing through the expected states (2WAY, EXSTART) and reaching FULL after receiving a Database Description (DBD) packet. This confirms that OSPF Hello and DBD packets are being processed normally, which means Control Plane Policing (CoPP) is not dropping OSPF traffic. CoPP would typically drop packets at the control plane, preventing state transitions like 2WAY or FULL.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
OSPF adjacency is failing due to CoPP dropping Hello packets.
Why it's wrong here
The output shows successful Hello exchange and transition to FULL state.
- ✓
OSPF adjacency is established successfully, indicating CoPP is not blocking OSPF traffic.
Why this is correct
The adjacency reached FULL state, meaning OSPF packets are being processed correctly.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
OSPF is experiencing packet loss due to MTU mismatch.
Why it's wrong here
The MTU of 1500 is mentioned, but no errors are indicated.
- ✗
OSPF is stuck in EXSTART state due to CoPP.
Why it's wrong here
The output shows transition from EXSTART to FULL.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that any debug output showing OSPF packet reception implies a problem, when in fact the sequence of states (2WAY to FULL) indicates successful adjacency formation, and candidates may incorrectly attribute normal behavior to CoPP failure.
Trap categories for this question
Command / output trap
The output shows successful Hello exchange and transition to FULL state.
Detailed technical explanation
How to think about this question
OSPF adjacency formation requires successful exchange of Hello packets for neighbor discovery (2WAY), followed by DBD packets for database synchronization (EXSTART/EXCHANGE). CoPP applies QoS policies to control plane traffic; if OSPF packets were rate-limited or dropped, the adjacency would fail to form or remain in INIT/2WAY. The debug output confirms all OSPF packet types (Hello, DBD) are processed, ruling out CoPP interference. In real-world scenarios, CoPP misconfiguration often causes intermittent OSPF flaps, which would show repeated state transitions or timeouts in debugs.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
What to study next
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FAQ
Questions learners often ask
What does this 300-410 question test?
Control Plane Policing (CoPP) — This question tests Control Plane Policing (CoPP) — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: OSPF adjacency is established successfully, indicating CoPP is not blocking OSPF traffic. — The debug output shows the OSPF adjacency progressing through the expected states (2WAY, EXSTART) and reaching FULL after receiving a Database Description (DBD) packet. This confirms that OSPF Hello and DBD packets are being processed normally, which means Control Plane Policing (CoPP) is not dropping OSPF traffic. CoPP would typically drop packets at the control plane, preventing state transitions like 2WAY or FULL.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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