- A
OSPFv3 will not form adjacencies because the router-id must be an IPv6 address.
Why wrong: OSPFv3 router-id is a 32-bit number in dotted-decimal format, not an IPv6 address. 4.4.4.4 is a valid router-id.
- B
OSPFv3 will only form adjacency on GigabitEthernet0/0 because the router-id is not configured under the interface.
Why wrong: The router-id is configured globally under the OSPFv3 process, which is sufficient. It does not need to be per-interface.
- C
OSPFv3 will form adjacencies on both interfaces as intended because the router-id is correctly set and OSPFv3 is enabled on each interface.
The configuration is correct: router-id is set, interfaces are enabled for OSPFv3 in area 0. OSPFv3 will operate normally.
- D
OSPFv3 will not form any adjacency because the network type is not specified.
Why wrong: The default network type for Ethernet interfaces is broadcast, which is fine for OSPFv3. No explicit network type is required.
OSPFv3: Setting Router-ID for IPv6 OSPF
This 300-410 practice question tests your understanding of device management. 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.
Consider the following partial configuration on router R4:
interface GigabitEthernet0/0 ip address 192.168.2.1 255.255.255.0
ipv6 address 2001:db8:1::1/64 ipv6 ospf 1 area 0 !
interface GigabitEthernet0/1 ip address 10.0.0.1 255.255.255.0
ipv6 address 2001:db8:2::1/64 ipv6 ospf 1 area 0 ! ipv6 router ospf 1 router-id 4.4.4.4
What is the effect of this configuration?
Quick Answer
The answer is that OSPFv3 will form adjacencies on both interfaces as intended because the router-id is correctly set and OSPFv3 is enabled on each interface. This configuration works because OSPFv3, unlike OSPFv2, cannot automatically derive a router-id from an IPv4 interface address; it must be explicitly configured under the OSPFv3 process with the router-id command, or it will fail to start. In this case, the router-id 4.4.4.4 is manually defined, and both GigabitEthernet interfaces have ipv6 ospf 1 area 0 enabled, allowing OSPFv3 to form neighbor relationships over IPv6. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding that a missing or invalid router-id is a common misconfiguration trap—many candidates assume OSPFv3 will auto-select an IPv4 address, but it does not. A helpful memory tip: “OSPFv3 needs a manual ID, or OSPF won’t proceed.”
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
OSPFv3 will form adjacencies on both interfaces as intended because the router-id is correctly set and OSPFv3 is enabled on each interface.
Option C is correct because OSPFv3 (OSPF for IPv6) uses a 32-bit router-id, which can be an IPv4 address (like 4.4.4.4) or any arbitrary 32-bit value, and does not require an IPv6 address. The configuration enables OSPFv3 process 1 under the global 'ipv6 router ospf 1' command, sets the router-id, and activates OSPFv3 on both interfaces with 'ipv6 ospf 1 area 0', allowing adjacencies to form normally on both GigabitEthernet0/0 and GigabitEthernet0/1.
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.
- ✗
OSPFv3 will not form adjacencies because the router-id must be an IPv6 address.
Why it's wrong here
OSPFv3 router-id is a 32-bit number in dotted-decimal format, not an IPv6 address. 4.4.4.4 is a valid router-id.
- ✗
OSPFv3 will only form adjacency on GigabitEthernet0/0 because the router-id is not configured under the interface.
Why it's wrong here
The router-id is configured globally under the OSPFv3 process, which is sufficient. It does not need to be per-interface.
- ✓
OSPFv3 will form adjacencies on both interfaces as intended because the router-id is correctly set and OSPFv3 is enabled on each interface.
Why this is correct
The configuration is correct: router-id is set, interfaces are enabled for OSPFv3 in area 0. OSPFv3 will operate normally.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
OSPFv3 will not form any adjacency because the network type is not specified.
Why it's wrong here
The default network type for Ethernet interfaces is broadcast, which is fine for OSPFv3. No explicit network type is required.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that OSPFv3 requires an IPv6 router-id, when in fact it uses a 32-bit router-id (like an IPv4 address), and candidates may also incorrectly assume that OSPFv3 needs per-interface router-id configuration or explicit network type statements.
Detailed technical explanation
How to think about this question
OSPFv3 (RFC 5340) separates the protocol's transport from the IPv6 address family, using link-local addresses for neighbor discovery and a 32-bit router-id for router identification, which can be an IPv4 address or any unique 32-bit value. In real-world scenarios, if the router-id is not manually set, OSPFv3 will automatically select the highest IPv4 address on a loopback or physical interface; if no IPv4 address exists, the process fails to start, making manual configuration critical in IPv6-only networks. Additionally, OSPFv3 uses the same area concept and SPF algorithm as OSPFv2, but with different LSA types and flooding scopes.
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?
Device Management — This question tests Device Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: OSPFv3 will form adjacencies on both interfaces as intended because the router-id is correctly set and OSPFv3 is enabled on each interface. — Option C is correct because OSPFv3 (OSPF for IPv6) uses a 32-bit router-id, which can be an IPv4 address (like 4.4.4.4) or any arbitrary 32-bit value, and does not require an IPv6 address. The configuration enables OSPFv3 process 1 under the global 'ipv6 router ospf 1' command, sets the router-id, and activates OSPFv3 on both interfaces with 'ipv6 ospf 1 area 0', allowing adjacencies to form normally on both GigabitEthernet0/0 and GigabitEthernet0/1.
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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