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300-410 Practice Question: A large enterprise network is experiencing…
A large enterprise network is experiencing intermittent loss of connectivity to a subnet 10.10.10.0/24 from remote sites. Router R1 has the following relevant configuration: interface GigabitEthernet0/0 ip address 10.1.1.1 255.255.255.252 ip ospf 1 area 0 interface GigabitEthernet0/1 ip address 10.2.2.1 255.255.255.252 ip ospf 1 area 1 router ospf 1 area 1 range 10.10.0.0 255.255.248.0 Router R2 shows: show ip route 10.10.10.0 Routing entry for 10.10.8.0/21 Known via "ospf 1", distance 110, metric 20, type inter-area Last update from 10.1.1.2 on GigabitEthernet0/0, 00:05:32 ago What is the root cause?
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 summary route 10.10.8.0/21 does not include 10.10.10.0/24; adjust the area range to 10.10.0.0/20.
The area range configured on R1 is 10.10.0.0/21 (255.255.248.0), which only covers networks 10.10.0.0 through 10.10.7.255. The subnet 10.10.10.0/24 falls outside this range. As a result, when R1 summarizes routes from area 1 into area 0, it does not generate a summary that includes 10.10.10.0/24. The summary route 10.10.8.0/21 seen on R2 is coming from a different source or is a default summary; it does not correspond to the misconfigured range. The correct fix is to change the area range to 10.10.0.0/20 (255.255.240.0) to encompass the subnet.
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 summary route 10.10.8.0/21 does not include 10.10.10.0/24; adjust the area range to 10.10.0.0/20.
Why this is correct
The range 10.10.8.0/21 covers 10.10.8.0 to 10.10.15.255, missing 10.10.10.0/24. A /20 range would include it.
- ✗
The metric of 20 indicates a redistribution issue; check redistributed routes.
Why it's wrong here
The metric 20 is normal for inter-area routes; redistribution is not indicated here.
- ✗
The OSPF network type on GigabitEthernet0/0 is causing adjacency issues; change to point-to-point.
Why it's wrong here
The adjacency is established (route learned), so network type is not the issue.
- ✗
The area 1 range command is misconfigured with the wrong area; it should be area 0.
Why it's wrong here
Summarization is applied in the area where routes originate, area 1, not area 0.
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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