- A
Prepend AS 65000 multiple times on R2's updates to ISP2.
Correct because AS_PATH prepending makes the path through R2 longer, so ISP2 will prefer the path through ISP1, directing traffic to R1.
- B
Set a higher MED on R1's updates to ISP1.
Why wrong: Incorrect because MED is only compared within the same AS; ISP1 and ISP2 are different ASes, so MED from R1 will not influence ISP2's path selection.
- C
Set a higher local preference on R1 for routes learned from ISP1.
Why wrong: Incorrect because local preference influences outbound traffic from the enterprise, not inbound traffic from the Internet.
- D
Use the no-export community on R1's updates to ISP1.
Why wrong: Incorrect because the no-export community prevents the route from being advertised to eBGP peers, which would stop ISP1 from advertising the prefix, not influence path selection.
350-401 BGP Practice Question
This 350-401 practice question tests your understanding of bgp. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
An enterprise has two BGP routers, R1 and R2, both in AS 65000. R1 peers with ISP1 (AS 100) and R2 peers with ISP2 (AS 200). The enterprise advertises a prefix 192.168.0.0/24 to both ISPs. The engineer wants to ensure that traffic from the Internet to this prefix enters the network primarily via R1, and only uses R2 if the link to ISP1 fails. Which BGP attribute should be manipulated on the updates sent to the ISPs?
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
Prepend AS 65000 multiple times on R2's updates to ISP2.
To influence inbound traffic from the Internet, you must manipulate attributes sent to the ISPs. AS path prepending makes a route appear less preferred by artificially lengthening the AS path. By prepending AS 65000 multiple times on R2's updates to ISP2, ISP2 will see a longer AS path for the prefix and prefer the shorter path via ISP1, causing traffic to enter primarily via R1 unless the ISP1 link fails.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Prepend AS 65000 multiple times on R2's updates to ISP2.
Why this is correct
Correct because AS_PATH prepending makes the path through R2 longer, so ISP2 will prefer the path through ISP1, directing traffic to R1.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Set a higher MED on R1's updates to ISP1.
Why it's wrong here
Incorrect because MED is only compared within the same AS; ISP1 and ISP2 are different ASes, so MED from R1 will not influence ISP2's path selection.
- ✗
Set a higher local preference on R1 for routes learned from ISP1.
Why it's wrong here
Incorrect because local preference influences outbound traffic from the enterprise, not inbound traffic from the Internet.
- ✗
Use the no-export community on R1's updates to ISP1.
Why it's wrong here
Incorrect because the no-export community prevents the route from being advertised to eBGP peers, which would stop ISP1 from advertising the prefix, not influence path selection.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between attributes that influence inbound vs. outbound traffic; the trap here is confusing local preference (outbound) with AS path prepending (inbound), leading candidates to incorrectly choose local preference manipulation.
Detailed technical explanation
How to think about this question
AS path prepending works by adding repeated copies of the local AS number to the AS_PATH attribute, making the route appear longer to downstream ISPs. BGP path selection prefers the shortest AS path, so prepending effectively makes the route less attractive. In real-world scenarios, ISPs may also apply local policies, but prepending remains a common, lightweight method for traffic engineering across multiple providers.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 350-401 question test?
BGP — This question tests BGP — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Prepend AS 65000 multiple times on R2's updates to ISP2. — To influence inbound traffic from the Internet, you must manipulate attributes sent to the ISPs. AS path prepending makes a route appear less preferred by artificially lengthening the AS path. By prepending AS 65000 multiple times on R2's updates to ISP2, ISP2 will see a longer AS path for the prefix and prefer the shorter path via ISP1, causing traffic to enter primarily via R1 unless the ISP1 link fails.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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