Question 22 of 2,011
mediumMultiple ChoiceObjective-mapped
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
The LS Type is Summary Links, not Router Links.
- ✓
It is a summary route for 172.16.0.0/20 advertised by ABR 2.2.2.2.
Why this is correct
This Type 3 LSA advertises a summary route for 172.16.0.0/20 from ABR 2.2.2.2.
- ✗
It is an external route from ASBR.
Why it's wrong here
Type 5 LSAs are external; this is Type 3.
- ✗
It is a network LSA for the 172.16.0.0 network.
Why it's wrong here
Network LSA is Type 2, not Type 3.
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: The 'show ip route summary' command provides a summary of the routing table including the number of routes and the memory used, while 'show ip ospf border-routes' displays the OSPF route table entries for ABRs and ASBRs, which can include summary routes. 'show ip protocols' does not directly show summarization details. 'show ip route' alone does not summarize. 'show ip ospf database' shows the LSDB, not the summarized routing table.
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.
Last reviewed: Jun 18, 2026
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