mediumMultiple Choice
300-410 Practice Question: Runs the following command on Router R1: R1# show…
A network engineer runs the following command on Router R1:
R1# show ip ospf database summary 172.16.0.0
OSPF Router with ID (1.1.1.1) (Process ID 1)
Summary Net Link States (Area 0)
LS age: 100 Options: (No TOS-capability, DC) LS Type: Summary Links(Network) Link State ID: 172.16.0.0 (Summary Network Number) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0x1234 Length: 28 Network Mask: /20 TOS: 0 Metric: 10
Based on this output, what does this LSA represent?
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
✓
It is a summary route for 172.16.0.0/20 advertised by ABR 2.2.2.2.
This is a Type 3 Summary LSA, which is used to advertise inter-area routes. The Advertising Router is 2.2.2.2, an ABR.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It is a router LSA from R1.
Why it's wrong here
Router LSAs (Type 1) are generated by every OSPF router for its own links within an area and are flooded intra-area, not advertised by 2.2.2.2 into Area 0 as a Summary Net Link State. It is tempting because R1 displays the database, but the LS Type field explicitly identifies a summary network LSA.
- ✓
It is a summary route for 172.16.0.0/20 advertised by ABR 2.2.2.2.
Why this is correct
The Type 3 summary LSA carries Link State ID 172.16.0.0 with Network Mask /20, giving the prefix 172.16.0.0/20. Advertising Router 2.2.2.2 identifies the ABR that generated it, and the Summary Net Link States (Area 0) heading confirms inter-area propagation into Area 0.
- ✗
It is an external route from ASBR.
Why it's wrong here
External routes are carried in Type 5 (or Type 7) LSAs originated by an ASBR and flagged as AS External, not Summary Net Link States. It is tempting because 2.2.2.2 advertises the prefix, but the LS Type confirms an inter-area summary generated by an ABR.
- ✗
It is a network LSA for the 172.16.0.0 network.
Why it's wrong here
Network LSAs (Type 2) are generated by the designated router for multi-access segments and carry the DR's interface address as Link State ID, not a network number with a /20 mask. It is tempting because the entry describes a network, but the LS Type is Summary Links(Network), a Type 3 LSA.
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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Same concept, more angles
3 more ways this is tested on 300-410
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which TWO commands can be used to verify route summarization on a Cisco router running OSPF? (Choose TWO.)
medium- ✓ A.show ip route summary
- ✓ B.show ip ospf border-routes
- C.show ip protocols
- D.show ip route
- E.show ip ospf database
Why A: Option A, 'show ip route summary', is correct because it displays the routing table statistics including the number of routes and, importantly, the number of routes learned per protocol, allowing you to confirm that OSPF summary routes are present and reducing the route count. Option B, 'show ip ospf border-routes', is correct because it shows the ABR (Area Border Router) and ASBR (Autonomous System Boundary Router) border routers, which is relevant for verifying summarization since summarization is typically performed on ABRs or ASBRs and this command helps confirm the router's role in the OSPF topology. Option C, 'show ip protocols', is incorrect because it displays routing protocol parameters and timers but does not directly show route summarization information. Option D, 'show ip route', is incorrect because while it shows the routing table, it does not specifically verify summarization; it only lists individual routes. Option E, 'show ip ospf database', is incorrect because it displays the OSPF link-state database (LSAs) and does not directly verify route summarization on the router.
Variation 2. A network engineer runs the following command on Router R1: R1# show ip route 172.16.0.0 255.255.240.0 Routing entry for 172.16.0.0/20 Known via "ospf 1", distance 110, metric 20, type intra area Last update from 192.168.1.2 on GigabitEthernet0/0, 00:00:15 ago Routing Descriptor Blocks: * 192.168.1.2, from 192.168.1.2, 00:00:15 ago, via GigabitEthernet0/0 Route metric is 20, traffic share count is 1 Based on this output, what can be concluded about the route 172.16.0.0/20?
medium- A.The route is a default route.
- ✓ B.The route is an inter-area summary route.
- C.The route is an external route.
- D.The route is a connected route.
Why B: The route 172.16.0.0/20 is learned via OSPF with type 'intra area', which indicates it is an intra-area route, not a summary. Intra-area routes are learned via Type 1 or Type 2 LSAs. The metric of 20 is typical for an OSPF intra-area route. Therefore, none of the given options correctly describe this route: it is not a default route (A), not an inter-area summary (B), not an external route (C), and not a connected route (D).
Variation 3. A network engineer runs the following command on Router R1: R1# show ip route summary IP routing table maximum-paths: 32 IP routing table has 15 routes, using 900 bytes of memory Number of prefixes: /8: 1, /16: 2, /20: 3, /24: 9 Route types: Connected: 4, Static: 1, OSPF: 10 Route sources: OSPF: 10, Connected: 4, Static: 1 Based on this output, what is a potential issue regarding route summarization?
hard- A.The routing table is too small.
- ✓ B.There are too many /24 prefixes, suggesting poor summarization.
- C.There are too many OSPF routes.
- D.The routing table is empty.
Why B: The routing table has many /24 prefixes (9), indicating that route summarization is not being used effectively, leading to a larger routing table.
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.