300-320 Question #138: Real Exam Question with Answer & Explanation

The correct answer is A: AS path. Inbound traffic engineering means influencing how external ASes send traffic to you - you must manipulate attributes that are visible and meaningful to your upstream peers. A (AS path prepending) is correct: By artificially lengthening your AS path on announcements sent through t

Question

A network engineer is designing a dual router, dual ISP solution and must prefer one ISP for inbound traffic over the other. Which two BGP attributes can be manipulated to accomplish this goal? (Choose two.)

Options

AAS path
BMED
Clocal preference
Dweight
Eorigin code

Explanation

Inbound traffic engineering means influencing how external ASes send traffic to you - you must manipulate attributes that are visible and meaningful to your upstream peers. A (AS path prepending) is correct: By artificially lengthening your AS path on announcements sent through the less-preferred ISP, you make that path look longer to the rest of the internet, causing remote ASes to prefer the other ISP's path to reach you. B (MED) is correct: MED (Multi-Exit Discriminator) is advertised to a directly connected neighboring AS to signal which of your entry points you prefer. It influences inbound traffic from that specific neighbor. C (Local preference) is incorrect - it is used internally within your own AS to influence outbound path selection and is not sent to external peers. D (Weight) is incorrect - it is Cisco-proprietary, locally significant to a single router only, and controls outbound path selection. E (Origin code) is incorrect - it is not used for traffic engineering purposes.

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