The answer is to set a higher local preference on routes advertised to the customer from the desired entry point, typically using a BGP community like 2:100. This works because local preference is the first BGP attribute checked in the inbound decision process; by tagging routes with a community that instructs the customer’s router to assign a higher local preference (e.g., 200), you make that entry point the most preferred path for traffic entering your AS from the customer. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding of BGP path selection and community-based policy propagation—a common trap is confusing inbound traffic engineering with outbound tools like AS-path prepending, which only influences traffic leaving the customer. Remember, to pull traffic in, you must raise local preference on the routes you send out. Memory tip: “Inbound = Inflate LP on outbound updates.”
350-501 Networking Practice Question
This 350-501 practice question tests your understanding of networking. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
A service provider wants to influence inbound traffic from a customer AS. The customer AS is multi-homed to two provider ASes. Which BGP community is most effective to make the customer prefer a specific entry point?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Set community 'local-preference 200' on routes from the desired entry point.
The provider can set the 'prepend' community (e.g., 100:1) to request the customer to prepend AS path, but that is outbound. To influence inbound, the provider should use communities that affect the customer's BGP decision process, like local preference. However, the most effective is to set a higher local preference on routes advertised to the customer from the desired entry point. This is typically done via the 'local-preference' community (e.g., 2:100).
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Set community 'no-export' on routes from the undesired entry point.
Why it's wrong here
No-export prevents routes from leaving the AS; not effective for inbound influence.
✗
Set community 'prepend 3' on routes from the desired entry point.
Why it's wrong here
Prepending would make the AS path longer, less preferred.
✓
Set community 'local-preference 200' on routes from the desired entry point.
Why this is correct
This community instructs the customer to set local preference higher for those routes, making that entry point preferred.
Related concept
Static NAT maps one inside address to one outside address.
✗
Set community 'no-advertise' on routes from the undesired entry point.
Why it's wrong here
No-advertise prevents advertisement to any peer; too restrictive.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-501 NAT questions on configuration and troubleshooting.
Networking — This question tests Networking — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Set community 'local-preference 200' on routes from the desired entry point. — The provider can set the 'prepend' community (e.g., 100:1) to request the customer to prepend AS path, but that is outbound. To influence inbound, the provider should use communities that affect the customer's BGP decision process, like local preference. However, the most effective is to set a higher local preference on routes advertised to the customer from the desired entry point. This is typically done via the 'local-preference' community (e.g., 2:100).
What should I do if I get this 350-501 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-501 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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