350-501 Networking Practice Question
In BGP confederation, how does the AS_PATH attribute handle the confederation sub-AS numbers to prevent loops?
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
✓
Confederation sub-AS numbers are carried in a separate confederation AS_PATH segment and are stripped when routes leave the confederation
In BGP confederation, confederation sub-AS numbers are carried in a separate confederation AS_PATH segment and are not visible to external BGP peers. The confederation AS_PATH is used for loop prevention within the confederation, while the regular AS_PATH remains unchanged when routes leave the confederation.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Confederation sub-AS numbers are added to the regular AS_PATH
Why it's wrong here
They are added to a separate confederation AS_PATH segment, not the regular AS_PATH.
- ✓
Confederation sub-AS numbers are carried in a separate confederation AS_PATH segment and are stripped when routes leave the confederation
Why this is correct
Correct. The confederation AS_PATH is used within the confederation and removed when routes are advertised outside.
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Confederation sub-AS numbers are replaced by the confederation identifier
Why it's wrong here
The confederation identifier is used as the AS number to external peers, but sub-AS numbers are not replaced.
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Confederation sub-AS numbers are ignored for loop detection
Why it's wrong here
They are used for loop detection within the confederation.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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