350-401 · Question #305
Drag and Drop Question Drag and Drop the decryptions from the left onto the routing protocol they describe on the right. Answer:
The correct answer is summaries can be created in specific parts of the IGP topology; uses areas to segment a network; DUAL algorithm; summaries can be created anywhere in the IGP topology. Routing Protocol Drag-and-Drop Explanation This question matches descriptions to two IGP routing protocols: OSPF and EIGRP. --- Correct Mapping | Position | Description | Protocol | |----------|-------------|----------| | 1 | summaries can be created in specific parts of the IGP
Question
Exhibits
Answer Area
Drag items
Correct arrangement
- summaries can be created in specific parts of the IGP topology
- uses areas to segment a network
- DUAL algorithm
- summaries can be created anywhere in the IGP topology
Explanation
Routing Protocol Drag-and-Drop Explanation
This question matches descriptions to two IGP routing protocols: OSPF and EIGRP.
Correct Mapping
| Position | Description | Protocol |
|---|---|---|
| 1 | summaries can be created in specific parts of the IGP topology | OSPF |
| 2 | uses areas to segment a network | OSPF |
| 3 | DUAL algorithm | EIGRP |
| 4 | summaries can be created anywhere in the IGP topology | EIGRP |
Item-by-Item Reasoning
1. "Summaries can be created in specific parts of the IGP topology" -> OSPF In OSPF, route summarization is only permitted at Area Border Routers (ABRs) and Autonomous System Boundary Routers (ASBRs). Internal routers cannot summarize routes. This is a fundamental architectural constraint of OSPF.
2. "Uses areas to segment a network" -> OSPF OSPF's defining structural feature is its hierarchical area design - Area 0 (backbone) plus subordinate areas. This reduces LSA flooding and limits topology database size. EIGRP has no concept of areas.
3. "DUAL algorithm" -> EIGRP The Diffusing Update Algorithm (DUAL) is EIGRP's core routing algorithm. It guarantees loop-free paths and fast convergence by maintaining feasible successors. This is unique to EIGRP - OSPF uses Dijkstra's SPF algorithm.
4. "Summaries can be created anywhere in the IGP topology" -> EIGRP EIGRP allows manual summarization on any router interface, not just boundary routers. This gives network engineers granular control over route aggregation throughout the topology.
Common Mistakes
- Confusing summarization rules: Students often forget OSPF restricts summarization to ABRs/ASBRs. EIGRP's flexibility here is a key differentiator.
- Attributing areas to EIGRP: EIGRP does not use areas. Only OSPF (and IS-IS) use hierarchical area structures.
- DUAL vs SPF: DUAL is exclusively EIGRP. OSPF runs Dijkstra's Shortest Path First (SPF) - never confuse the two.
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