300-420 Question 23
Select 3An organization is designing a BGP-based multi-homed architecture to connect to two different ISPs for redundancy and improved performance. The IT team wants to ensure that inbound traffic from the internet is distributed across both ISPs, but they also want to avoid creating routing instability. Which of the following design considerations should the team implement to achieve these goals?
- A
Advertise more specific prefixes to each ISP to control inbound traffic distribution.
- B
Use AS Path Prepending to influence inbound traffic paths.
- C
Configure BGP Route Reflectors to improve redundancy with ISPs.
- D
Implement BGP communities to tag routes for better policy control.
- E
Use the same MED (Multi-Exit Discriminator) value for all routes across both ISPs.
Show answer and explanation
Correct answers: A, B, D
Explanation
To achieve stable, secure, and scalable BGP routing designs, it is essential to use techniques like advertising specific prefixes, AS Path Prepending, and BGP communities. These methods provide fine-grained control over inbound traffic distribution while maintaining routing stability. Route Reflectors and MED values are not directly relevant to controlling inbound traffic from external ISPs in this scenario.
- A. Correct.
Advertising more specific prefixes allows the organization to control the traffic flow by influencing how ISPs route traffic back to their network. This helps distribute inbound traffic effectively.
- B. Correct.
AS Path Prepending is a common technique to influence inbound traffic by making certain paths appear longer, thereby steering traffic through preferred ISPs.
- C. Incorrect.
BGP Route Reflectors are used within an organization's internal BGP (iBGP) setup to avoid full mesh configurations. However, they do not address inbound traffic control or redundancy with external ISPs.
- D. Correct.
BGP communities allow tagging routes with specific attributes, which ISPs can use to apply policies. This provides greater control over how routes are treated, helping achieve traffic distribution and stability.
- E. Incorrect.
Using the same MED value across multiple ISPs does not influence inbound traffic, as MED is only relevant within the same AS or between neighbors in certain cases.