300-320 · Question #361
If your enterprise is connected to 2 ISP, which method could you use to prevent being used as a transit network? (Choose Two)
The correct answer is A. filter outbound E. Allow every routes inbound. To prevent your AS from being used as a transit network between two ISPs, the primary mechanism is outbound route filtering (A): you configure BGP to only advertise your own prefixes to each ISP, never re-advertising routes learned from one ISP to the other. This ensures…
Question
If your enterprise is connected to 2 ISP, which method could you use to prevent being used as a transit network? (Choose Two)
Options
- Afilter outbound
- Bfilter inbound
- Cthrow both ISP
- Dchoose only one ISP
- EAllow every routes inbound
How the community answered
(14 responses)- A71% (10)
- B7% (1)
- C7% (1)
- D14% (2)
Explanation
To prevent your AS from being used as a transit network between two ISPs, the primary mechanism is outbound route filtering (A): you configure BGP to only advertise your own prefixes to each ISP, never re-advertising routes learned from one ISP to the other. This ensures neither ISP can forward traffic through you toward the other. Accepting all routes inbound (E) is also part of this model-you receive full routing tables from both ISPs so your own traffic has optimal path selection, but since you control what you advertise outbound, you are never a transit path. Choice B (filter inbound) could limit your own routing visibility. Choices C and D do not address the transit prevention requirement technically.
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