Discuss Cisco 400-007 Exam Topic 5 Question 80

Refer to the exhibit.

An engineer has been asked to redesign the traffic flow toward AS 111 coming from AS 500. Traffic destined to AS 111 network 91.7.0.0/16 should come in via AS 100, while traffic destined to all other networks in AS 111 should continue to use the existing path. Which BGP attributes are best suited to control this inbound traffic coming from BGP AS 500 into the 91.7.0.0/16 network?

APrepend AS path for the 91.7.0.0/16 network and set it for neighbor in AS 200.

BUse extended community for the 91.7.0.0/16 network, not advertising it to the bi-lateral peer.

CUse local preference on R1 for the networks that AS 500 advertises to AS 111.

DSet higher MED for neighbor in AS 100 to influence incoming traffic for the 91.7.0.0/16 network.

Suggested Answer: A

Inbound traffic engineering is best controlled by manipulating how external ASes view your routes.

AS path prepending on the 91.7.0.0/16 prefix towards AS 200 makes AS 500 prefer the less-prepended path through AS 100.

This allows granular inbound control for that specific prefix while leaving the rest of the traffic unchanged.

Why other options are incorrect:

B: Extended community is not used for direct inbound path manipulation.

C: Local preference affects outbound traffic, not inbound path selection by remote ASes.

D: MED is only compared between the same AS; it won't affect AS 500's choice.

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23 comments · newest first

Socorro 2 days ago

But what about C? Local preference could also influence the routes effectively.

Gracia 7 days ago

I'm leaning towards A. Prepending AS path could help with the 91.7.0.0/16 network.

Denna 12 days ago

I agree! I think option D makes sense for controlling traffic.

Darrel 17 days ago

This question is tricky! I feel like it's testing our understanding of BGP attributes.

Junita 22 days ago

Same here! Let's hope for the best on the exam!

Harrison 27 days ago

Overall, I lean towards D for clarity in traffic flow.

Scarlet 1 month ago

I feel like B is too limiting. Not advertising could backfire.

Xuan 1 month ago

Right, local preference is more about outbound traffic.

Junita 1 month ago

C could be useful too, but not as direct as D.

Harrison 2 months ago

True, but it might complicate things.

Scarlet 2 months ago

But what about A? Prepending AS path could also work.

Xuan 2 months ago

I agree with Junita. It makes sense for AS 100.

Junita 2 months ago

I think D is the way to go. Higher MED can really influence traffic.

Harrison 2 months ago

This question is tricky! I feel unsure about the best option.

Cherelle 2 months ago

Wait, I didn't know MED could influence incoming traffic like that!

Felix 3 months ago

Prepending AS path might complicate things unnecessarily.

Jani 3 months ago

Isn't using extended community in option B a bit risky?

Wilburn 3 months ago

I disagree, I think option C is more effective for local routing.

Alease 3 months ago

Option D seems like the best choice for controlling inbound traffic.

Huey 3 months ago

I’m a bit confused about the extended community option; I don’t recall how it affects advertising to peers. Is it really the right choice for this case?

Antonio 3 months ago

I practiced a similar question where we had to manipulate MED values, so I feel like setting a higher MED for AS 100 might be a good strategy for this scenario.

Yoko 4 months ago

I think using local preference could help prioritize the traffic for 91.7.0.0/16, but I need to double-check how it interacts with other attributes.

Adelle 4 months ago

I remember something about using AS path prepending to influence traffic, but I'm not entirely sure if it's the best option here.

Cisco 400-007 Exam - Topic 5 Question 80 Discussion