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300-410 Practice Question: A large enterprise network is experiencing…
A large enterprise network is experiencing intermittent reachability to a subnet 10.1.1.0/24 from the rest of the network. Router R1 has the following relevant configuration:
router eigrp 100
redistribute ospf 1 metric 10000 100 255 1 1500 !
router ospf 1
redistribute eigrp 100 subnets summary-address 10.0.0.0 255.255.0.0 !
interface GigabitEthernet0/0 ip summary-address eigrp 100 10.0.0.0 255.255.0.0 5 Router R2 shows: R2# show ip route 10.1.1.0
Routing entry for 10.0.0.0/16, supernet Known via "eigrp 100", distance 90, metric 128256 Redistributing via eigrp 100 Last update from 10.10.10.1 on GigabitEthernet0/1
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 OSPF summary-address command on R1 is blocking the redistribution of the specific /24 route.
The issue is that R1 has both an OSPF summary-address and an EIGRP interface summary-address, causing the more specific /24 route to be suppressed by the /16 summary. The EIGRP summary-address command on the interface creates a null0 summary route, and the OSPF redistribution of the EIGRP summary further aggregates, losing the specific prefix. The fix is to remove the interface summary-address or adjust the summary to include the specific 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 OSPF summary-address command on R1 is blocking the redistribution of the specific /24 route.
Why this is correct
The OSPF summary-address creates an aggregate route, and combined with the EIGRP interface summary, the specific /24 is suppressed.
- ✗
The EIGRP metric values are too high, causing the route to be unreachable.
Why it's wrong here
The metric values are valid; the issue is summarization, not metric.
- ✗
The redistribute ospf command under EIGRP is missing the subnets keyword.
Why it's wrong here
The subnets keyword is present under OSPF redistribution, not needed under EIGRP.
- ✗
The route is being filtered by a distribute-list on R2.
Why it's wrong here
No distribute-list is configured; the issue is summarization.
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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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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