300-420 Question 217
Single answerAn enterprise network is connected to two separate Internet Service Providers (ISPs) for redundancy and improved availability. The network design team wants to ensure that outbound traffic uses one ISP as the primary path and the other ISP as a backup. Additionally, they require inbound traffic to be distributed across both ISPs to balance the load. Which approach should the design team implement to meet these requirements?
- A
Use BGP with AS Path Prepending for outbound traffic and BGP Communities for inbound traffic control.
- B
Implement Equal-Cost Multi-Path (ECMP) routing on both ISPs to handle outbound and inbound traffic equally.
- C
Configure Policy-Based Routing (PBR) for outbound traffic and rely on NAT to balance inbound traffic.
- D
Deploy a static default route for each ISP and use route metrics to determine primary and backup paths.
Show answer and explanation
Correct answer: A
Explanation
The combination of BGP with AS Path Prepending and BGP Communities is the most effective solution for achieving the desired traffic flow in a multihomed environment. AS Path Prepending allows the enterprise to prefer one ISP for outbound traffic while using the other as a backup. BGP Communities enable the enterprise to signal ISPs to influence inbound traffic flow, allowing for load balancing across both ISPs. This approach provides flexibility and scalability, making it the best choice for this scenario.
- A. Correct.
Using BGP with AS Path Prepending allows the enterprise to influence outbound traffic by making one path less preferred. BGP Communities can be used to signal ISPs to influence inbound traffic distribution, achieving the desired load balancing.
- B. Incorrect.
ECMP is typically used for equal distribution of traffic across multiple paths. However, it does not provide the required control to designate a primary and backup path for outbound traffic or balance inbound traffic.
- C. Incorrect.
Policy-Based Routing (PBR) can influence outbound traffic, but relying on NAT for inbound traffic balancing is not a scalable or effective solution in this scenario.
- D. Incorrect.
Static default routes with route metrics can establish primary and backup paths for outbound traffic, but they do not provide any method to control inbound traffic distribution.