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300-410 Practice Question: A redistribution setup between OSPF and EIGRP is…
A redistribution setup between OSPF and EIGRP is causing a routing loop for subnet 10.1.1.0/24. Router R1 runs OSPF and EIGRP with redistribution. R1's configuration:
router ospf 1
redistribute eigrp 100 subnets !
router eigrp 100
redistribute ospf 1 metric 10000 100 255 1 1500 !
interface GigabitEthernet0/0 ip address 10.1.1.1 255.255.255.0 ip summary-address eigrp 100 10.1.0.0 255.255.255.0
!
Router R2 (EIGRP neighbor) shows: R2# show ip route 10.1.1.0
Routing entry for 10.1.0.0/24, supernet Known via "eigrp 100", distance 90, metric 30720, type internal Last update from 10.1.1.1 on GigabitEthernet0/0, 00:00:05 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 10.1.0.0/24 is less specific and can cause routing loops when combined with redistribution because R2 may send traffic for 10.1.1.0/24 back to R1.
The summary route 10.1.0.0/24 is being advertised via EIGRP, but it is a less specific prefix than the actual /24. When R1 redistributes OSPF into EIGRP, the summary may cause R2 to prefer the summary over a more specific route, and if R2 sends traffic back to R1 for 10.1.1.0/24, R1 might forward it to R2 again if the OSPF route is not present, creating a loop. The summary should match the exact subnet or be more specific to avoid loops.
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 10.1.0.0/24 is less specific and can cause routing loops when combined with redistribution because R2 may send traffic for 10.1.1.0/24 back to R1.
Why this is correct
The summary creates a less specific route that can be redistributed, leading to a loop.
- ✗
The redistribution metric is too high, causing EIGRP to prefer the OSPF route via another path.
Why it's wrong here
Metric does not cause loops; it affects path selection.
- ✗
OSPF does not support subnets keyword, so the route is not redistributed correctly.
Why it's wrong here
The subnets keyword is correct for OSPF.
- ✗
EIGRP is not enabled on the interface, so the summary is not advertised.
Why it's wrong here
EIGRP is enabled via network command.
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
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.