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Exam 300-420 topic 1 question 38 discussion

Actual exam question from Cisco's 300-420

Question #: 38
Topic #: 1

Refer to the exhibit.

An engineer is designing a routing solution for a customer. The design must ensure that a failure of network 10.1.0.0/24, 10.1.2.0/24, 10.2.1.0/24, or 10.2.3.0/24 does not impact the core. It also requires fast convergence time during any link failover in the core or access networks.
Which solution must the engineer select?

A. Add aggregation layer between core and access networks.
B. Enable graceful restart on routers A and C.
C. Enable FRR for the connected networks of routers A and C.
D. Enable summarization on routers A and C.

Show Suggested Answer

Suggested Answer: D 🗳️

by cerifyme85 at March 24, 2023, 3:29 a.m.

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khazbimoas

3 weeks ago

Selected Answer: D

Correct is D. If 10.1.0.0/24, 10.1.2.0/24, 10.2.1.0/24, or 10.2.3.0/24 goes down, only the more-specific is withdrawn inside the access router. The /22 summary remains unchanged, so no query or route recomputation is triggered in the core EIGRP domain. C is wrong because FRR on connected networks – speeds data-plane failover on a single router only; it does not prevent EIGRP query storms or LSDB growth across the core.

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wolfone

4 months ago

Selected Answer: D

The best solution is to enable summarization on routers A and C. This way, individual /24 subnet failures (10.1.x.x and 10.2.x.x) do not cause routing changes in the core (which only sees the summarized routes), thereby reducing convergence times and limiting the impact of failures on the core. Fast Reroute (FRR) in EIGRP can provide sub-second convergence for link or node failures if there is an alternate path. However, FRR does not hide route withdrawals from the core if the subnet itself fails (and there is no redundant path to that subnet).

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wolfone

4 months ago

Selected Answer: D

Correct Answer: D

upvoted 2 times

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26d13e9

7 months, 3 weeks ago

Selected Answer: A

A......The FRR thing .....in order for it to be valid, it should not be only on routers A and C. On top of that, it still has impact (even though less but still has). Question says no impact. option A however, completely hide the impact from the core. Plus its mentioned everywhere in the cisco material.

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Clauster

1 year, 4 months ago

Selected Answer: C

The answers are B & C GraceFul Restart a feature in EIGRP that allows a router to gracefully restart without disrupting network traffic. When a router is configured for graceful restart, it will send a notification to its neighbors before it restarts. This allows the neighbors to prepare for the restart by building alternate routes to the networks that the router is advertising, it won't impact the core this way. For Fast Convergence: (FRR) is a feature in EIGRP that allows a router to quickly reroute traffic around a failed link. FRR uses a technique called Feasible Successors to pre-calculate backup routes that can be used in the event of a link failure.

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Emily23

1 year, 6 months ago

It is A. C?!... it is EIGRP. It uses DUAL. D? Pls review CCNA subnetting and summarizing before posting.

upvoted 2 times

Kacein

8 months ago

EIGRP Loop-Free Alternate (LFA) Fast Reroute (FRR) is a feature that allows EIGRP to switch to a backup path in less than 50 ms. Fast reroute means we switch to another next hop, Loop-free alternate is an alternative path in the network that is loop free. Now you might be thinking that this sounds familiar. After all, EIGRP has feasible successors. Those are loop-free alternate paths that EIGRP has calculated. If the successor fails, EIGRP can use a feasible successor right away. This is true, but there’s one big “gotcha”. EIGRP feasible successors are not installed in the routing table right away. Only the successor route is installed. When the successor fails, EIGRP installs the feasible successor, and this takes time. Fast reroute installs both the successor route and the feasible successor route in the routing table which makes convergence even faster.

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SpicyMochi

1 year, 7 months ago

Selected Answer: C

C. Enable FRR for the connected networks of routers A and C is the solution that the engineer should select. FRR (Fast Reroute) is a mechanism that provides fast convergence times during any link or node failure. It works by precomputing alternate backup paths that can be used in case of a failure, eliminating the need for the router to go through a time-consuming SPF calculation. In this scenario, enabling FRR on the connected networks of routers A and C ensures that any failure of network 10.1.0.0/24, 10.1.2.0/24, 10.2.1.0/24, or 10.2.3.0/24 will not impact the core, and fast convergence time will be achieved during any link failover in the core or access networks.

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cerifyme85

1 year, 9 months ago

Selected Answer: A

I think the answer should be A and D

upvoted 1 times

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