300-410 Layer 3 Technologies Practice Question
A network engineer is configuring BGP on a Cisco IOS XE router. The router has two eBGP peers: ISP-A and ISP-B. The engineer wants to influence outbound traffic so that the router prefers ISP-A for all destinations unless ISP-A fails. Which BGP attribute should the engineer manipulate, and how?
⚠ Common exam trap
A common mix-up: candidates confuse outbound and inbound traffic engineering, and mixing up attributes like MED and AS path prepending that affect inbound traffic.
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
✓
Set a higher local preference for routes learned from ISP-A using a route map with `set local-preference 200`.
Local preference is the correct attribute to influence outbound traffic in BGP. It is exchanged within an autonomous system via IBGP and is evaluated before MED and AS path. By assigning a higher local preference to routes from ISP-A, the router will consistently prefer ISP-A for outbound traffic as long as those routes are available. This provides a deterministic outbound path selection that can be applied network-wide.
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 the AS path for routes learned from ISP-A using a route map with `set as-path prepend`.
Why it's wrong here
AS path prepending adds additional autonomous system numbers to the AS_PATH attribute, making the path longer and less preferred. This influences inbound traffic from other autonomous systems, not outbound traffic from the local router. If applied to routes learned from ISP-A, it would make ISP-A less preferred for outbound traffic, which is the opposite of the desired outcome. Therefore, this is not the correct approach.
- ✗
Set a higher weight for routes learned from ISP-A using the `neighbor weight` command.
Why it's wrong here
Weight is a Cisco-proprietary attribute local to the router and is the highest in the best-path selection process. While setting a higher weight for ISP-A would indeed make those routes preferred, the command `neighbor weight` applies weight to all routes learned from that neighbor. However, the question asks which attribute should be manipulated to influence outbound traffic; local preference is the standards-based, network-wide attribute for this purpose. Weight is local to the router and not propagated, so it is less suitable for consistent outbound policy across an AS.
- ✓
Set a higher local preference for routes learned from ISP-A using a route map with `set local-preference 200`.
Why this is correct
Local preference is the second BGP attribute in the best-path selection process, after weight, and it is used to influence outbound traffic within an autonomous system. By setting a higher local preference for routes learned from ISP-A, the router will prefer those routes over routes from ISP-B for the same prefix. This is the standard method to control outbound path selection when multiple eBGP peers exist.
- ✗
Set a lower multi-exit discriminator (MED) for routes learned from ISP-A using a route map with `set metric 50`.
Why it's wrong here
MED is used to influence inbound traffic from an external autonomous system by suggesting a preferred entry point. It is compared only between routes from the same neighboring AS and is lower in the best-path selection order than local preference. Setting a lower MED for ISP-A would not affect the local router's outbound decision, which is governed by local preference first. Thus, it does not achieve the goal.
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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
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.