hardMultiple Select
300-410 Practice Question: Which TWO statements correctly describe the…
Which TWO statements correctly describe the behavior of EIGRP route summarization when using the 'summary-address' command under an interface? (Choose TWO.)
⚠ Common exam trap
300-410 often tests the misconception that EIGRP summarization advertises component routes alongside the summary, when in fact the summary suppresses the more specific routes out that interface.
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
✓
A summary route is advertised with the metric equal to the best metric among the component routes.
Option A is correct because when EIGRP advertises a summary route configured with the interface-level summary-address command, the summary inherits the minimum (best) metric among the component routes it covers, so the advertised metric reflects the most favorable path. Option C is correct because EIGRP automatically installs a discard route pointing to Null0 for the summary prefix on the summarizing router, which prevents the router from forwarding traffic for unallocated subnets within the summary and thus avoids routing loops. Option B is incorrect because administrative distance is a local routing-table preference (EIGRP internal is 90) and is not assigned to an advertised summary route by the summary-address command. Option D is incorrect because the interface summary-address command summarizes EIGRP-learned routes, not connected routes, which must be redistributed into EIGRP to be summarized. Option E is incorrect because, by default, the more specific component routes are suppressed from being advertised out the interface where the summary is configured.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
A summary route is advertised with the metric equal to the best metric among the component routes.
Why this is correct
The summary route inherits the minimum, or best, metric among its component routes. EIGRP advertises this single metric for the aggregate, so downstream routers reach all covered subnets through the summarising router, matching the stated metric behaviour.
- ✗
The summary route is automatically assigned an administrative distance of 90 by default.
Why it's wrong here
EIGRP summary routes created by summary-address are installed with an administrative distance of 5, not 90; 90 applies to internal EIGRP routes. The option tempts because 90 is EIGRP's well-known default AD, but that value governs learned internal routes rather than the locally generated summary.
- ✓
A local discard route (null0) is automatically installed for the summary prefix to prevent routing loops.
Why this is correct
Configuring summary-address causes EIGRP to install a null0 discard route for the summary prefix on the summarising router. This prevents traffic for unadvertised component subnets from being forwarded and looping, satisfying the loop-prevention behaviour described.
- ✗
The 'summary-address' command also summarizes connected routes that fall within the summary range.
Why it's wrong here
The summary-address command suppresses the advertisement of component routes learned via EIGRP, but it does not summarise connected routes on the interface; those require a static summary pointing to Null0. It is tempting because summarisation conceptually groups all prefixes in a range, yet connected networks remain advertised individually.
- ✗
More specific routes are still advertised out the same interface even after the summary is configured.
Why it's wrong here
Configuring summary-address suppresses the more specific component routes from being advertised out that interface, leaving only the summary. It is tempting because EIGRP does advertise some specifics elsewhere, but on the summarised interface the components are filtered, which is the command's purpose.
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.
Go deeper
Related to this question
Learn chapter
EIGRP Route Summarization and Filtering
Key term
EIGRP Route Summarization
EIGRP route summarization is a technique that combines multiple specific network routes into one summary route to reduce routing table size and improve network stability.
Key term
BGP Route Aggregation
BGP Route Aggregation is a technique that combines multiple specific network routes into a single summary route to reduce the size of routing tables and improve network efficiency.
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Same concept, more angles
2 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. In EIGRP, what is the default behavior of auto-summary in IOS-XE versions 15.0 and later?
medium- A.Auto-summary is enabled by default.
- ✓ B.Auto-summary is disabled by default.
- C.Auto-summary is enabled only for EIGRP named mode.
- D.Auto-summary is disabled only for EIGRP classic mode.
Why B: Starting with Cisco IOS 15.0(1)M and IOS-XE 15.x, EIGRP auto-summary is disabled by default for both classic and named modes. This change aligned EIGRP with modern classless routing behavior and prevents the suboptimal routing caused by summarizing at classful boundaries.
Variation 2. A network engineer is troubleshooting a connectivity issue between two branches connected via a WAN link. Router R1 (10.1.0.0/16) is summarizing its directly connected subnets (10.1.1.0/24, 10.1.2.0/24, 10.1.3.0/24) as a single 10.1.0.0/16 route to Router R2 via EIGRP. Users at R2 report that they cannot reach the 10.1.4.0/24 subnet, which was recently added to R1. What is the most likely cause of the problem?
medium- A.The summary route 10.1.0.0/16 was configured manually, and the new subnet 10.1.4.0/24 is not within the summary range because the mask is too specific.
- ✓ B.The new subnet 10.1.4.0/24 was not advertised because the summary address command suppresses more specific routes, but the summary itself is not being generated due to a missing network statement under the EIGRP process.
- C.The WAN link is down, causing R2 to lose the summary route.
- D.The engineer forgot to configure the summary address on the interface facing R2 for the new subnet.
Why B: When EIGRP manual summarization is configured with the 'ip summary-address eigrp' command, the summary route is advertised only if at least one component subnet is present in the EIGRP topology table. If the summary is not being generated — for example, because the component networks are not being advertised into EIGRP due to a missing network statement — then the summary itself will not appear, and R2 will have no route to any 10.1.x.x subnet including the new 10.1.4.0/24.
JA
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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