mediumMultiple Select
350-401 Practice Question: Which three statements about OSPF route…
Which three statements about OSPF route summarization are true? (Choose three.)
⚠ Common exam trap
The trap is assuming OSPF can summarize any LSA type; candidates forget that Type 1 and Type 2 LSAs are intra-area and cannot be summarized, and that summarization is only performed on ABRs and ASBRs.
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
✓
Inter-area route summarization is configured on ABRs using the "area range" command.
Option A is correct because inter-area summarization is performed on Area Border Routers (ABRs) with the "area <area-id> range <ip> <mask>" command, which aggregates Type 3 summary LSAs advertised into other areas. Option B is correct because external route summarization is configured on Autonomous System Boundary Routers (ASBRs) using the "summary-address <ip> <mask>" command, which aggregates Type 5 (or Type 7) external LSAs. Option C is correct because summarization shrinks the link-state database and routing tables by replacing many specific prefixes with one aggregate, which reduces SPF computation overhead and speeds convergence. Option D is wrong because Type 1 router LSAs describe a router's own links and cannot be summarized, and summarization is not performed on arbitrary routers. Option E is wrong because OSPF summarization applies to Type 3 and Type 5/7 LSAs, not to Type 1 and Type 2 LSAs, which must remain intact within an area for topology accuracy.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Inter-area route summarization is configured on ABRs using the "area range" command.
Why this is correct
Inter-area summarisation is configured on area border routers with the **area** *range* command, which consolidates Type 3 summary LSAs for networks within a specified area. This satisfies the stem's requirement for a true OSPF summarisation statement, since ABRs generate inter-area prefixes and can suppress individual component routes.
- ✓
External route summarization is configured on ASBRs using the "summary-address" command.
Why this is correct
ASBRs generate Type 5 external LSAs, so summarising external destinations requires the summary-address command locally on the ASBR; this aggregates redistributed routes before flooding, satisfying the requirement that external summarisation occurs at the ASBR rather than on ABRs.
- ✓
Route summarization reduces the size of the LSDB and improves network convergence.
Why this is correct
Aggregated prefixes replace many individual LSAs, shrinking the link-state database each router stores and processes. Fewer LSAs mean less SPF computation and fewer topology changes to propagate, directly satisfying the stated benefit of smaller LSDB size and improved convergence.
- ✗
Route summarization can be configured on any OSPF router to reduce Type 1 LSAs.
Why it's wrong here
Summarisation is configured only on ABRs and ASBRs at area boundaries, not on any router, and it suppresses Type 3 or Type 5 LSAs rather than Type 1. It is tempting because Type 1 reduction sounds beneficial, but intra-area topology LSAs are not summarised.
- ✗
Summarization in OSPF can be applied to Type 1 and Type 2 LSAs to reduce flooding.
Why it's wrong here
OSPF summarisation applies to Type 3 and Type 5 LSAs generated at ABRs and ASBRs; Type 1 and Type 2 LSAs stay within an area and are never summarised. It is tempting because reducing flooding is desirable, but intra-area router and network LSAs cannot be aggregated.
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 and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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