Question 1easymultiple choice
Full question →easymultiple choiceObjective-mapped
Which OSPF component is used to identify routers uniquely inside an OSPF domain?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Distractor review
Area ID
Area IDs identify OSPF areas, not individual routers.
B
Best answer
Router ID
The router ID uniquely identifies an OSPF speaker.
C
Distractor review
Hello timer
Hello timers control neighbor keepalives.
D
Distractor review
Wildcard mask
Wildcard masks are used in OSPF network statements, not as unique router identifiers.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is mistaking the OSPF area ID for the router ID. While area IDs define logical groupings of routers within an OSPF domain, they do not uniquely identify individual routers. Another pitfall is confusing the router ID with the OSPF process ID, which is locally significant and does not uniquely identify routers. Additionally, some candidates incorrectly select hello timers or wildcard masks, which serve different purposes such as neighbor keepalive intervals and network statement definitions, respectively. Understanding these distinctions is critical to avoid selecting incorrect options that sound related but serve different functions.
Technical deep dive
How to think about this question
OSPF (Open Shortest Path First) is a link-state routing protocol that requires each router in an OSPF domain to have a unique identifier called the router ID. The router ID is a 32-bit value, typically represented in IPv4 address format, that uniquely identifies each OSPF router within the entire OSPF autonomous system. This identifier is crucial because OSPF routers exchange link-state advertisements (LSAs) that reference router IDs to build a consistent and loop-free topology database. The router ID is selected based on a specific priority order: first, a manually configured router ID; if none is configured, the highest IPv4 address assigned to a loopback interface; if no loopback exists, the highest IPv4 address on any active physical interface is used. This ensures that each router has a stable and unique ID that remains consistent across OSPF processes. The router ID is distinct from the OSPF process ID, which is locally significant and does not affect OSPF neighbor relationships or LSDB synchronization. A common exam trap is confusing the router ID with other OSPF parameters such as the area ID or hello timer. The area ID identifies OSPF areas, not routers, and hello timers control neighbor relationship maintenance. Misunderstanding these roles can lead to incorrect answers. Practically, the router ID is essential for OSPF operations like DR/BDR elections and LSA origination, making it a fundamental concept for both the CCNA exam and real-world OSPF deployments.
KKey Concepts to Remember
- OSPF uses a unique 32-bit router ID to identify each router within the entire OSPF autonomous system.
- The router ID is selected based on a priority: manually configured ID, highest loopback IPv4 address, or highest active interface IPv4 address.
- OSPF area IDs define logical groupings of routers but do not uniquely identify individual routers.
- Hello timers in OSPF control the frequency of hello packets to maintain neighbor relationships, not router identification.
- Wildcard masks are used in OSPF network statements to specify IP address ranges, not to identify routers uniquely.
- The OSPF process ID is locally significant and does not affect router identification or neighbor relationships.
- Router IDs are essential for OSPF functions such as DR/BDR elections and link-state advertisement origination.
- Confusing router ID with area ID or process ID is a common exam mistake that leads to incorrect answers.
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.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
OSPF uses a unique 32-bit router ID to identify each router within the entire OSPF autonomous system.
What is the correct answer to this question?
The correct answer is: Router ID — The router ID is the unique identifier OSPF uses for each router. It is not the same thing as the process ID, which is locally significant only.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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