1.3-BGP Path Attributes and Loop Prevention

Question 1

What are the four BGP path attributes?

Answer 1

• Well-known, Mandatory: Must be supported and propagated.
• Well-known, Discretionary: Must be supported; propagation optional.
• Optional, Transitive: Marked as partial if unsupported by a neighbor.
• Optional, Non-Transitive: Deleted if unsupported by a neighbor.

Question 2

What are the Metrics for Well-known, Mandatory attributes?

Answer 2

1. Origin: Origin type (IGP, EGP, or unknown).
2. AS-Path: List of autonomous systems which the advertisement has traversed.
3. Next-hop: External peer in neighboring AS.

Question 3

What are the Metrics for Well-known, Discretionary attributes?

Answer 3

• local Preference: Metric for internal neighbors to reach external destinations (default 100).
• Atomic Aggregate: Includes AS’s that have been dropped due to route aggregation.

Question 4

What are the Metrics for Optional, Transitive attributes?

Answer 4

• Aggregator: ID.
• AS of summarizing router.
• Community: Route tag.

Question 5

What are the Metrics for Optional, Non-Transitive attributes?

Answer 5

MED (Metric)
Originator ID
Cluster