1.3-BGP Path Attributes and Loop Prevention

Question 1

What are the four BGP path attributes?

Answer 1

Origin: Indicates how a route was learned (IGP, EGP, or Incomplete).
AS Path: Lists the sequence of Autonomous Systems (ASes) the route has traversed.
Next Hop: Specifies the next-hop IP address to reach the advertised prefix.
Local Preference: Influences outbound traffic by setting a preference for BGP paths within an AS (higher is preferred).

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: Influences outbound traffic within an AS (used for best path selection).
• Atomic Aggregate: Indicates that a less specific route was aggregated, causing loss of more specific routes.

Question 4

What are the Metrics for Optional, Transitive attributes?

Answer 4

Aggregator: Identifies the AS that aggregated routes.
Community: Used for route grouping and policy enforcement.
Originator ID: Used in Route Reflector environments to prevent routing loops.

Question 5

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

Answer 5

MED: Influences inbound traffic between two autonomous systems (ASes).
Origin Validation State: Determines if a prefix is legitimate based on ROA (Route Origin Authorization).