300-420 Question 22
Single answerAn enterprise network consists of multiple branch offices and a central data center. The branches are connected via MPLS links, and the data center connects to two different Internet Service Providers (ISPs) via BGP. The enterprise wants to ensure stable and scalable routing, with the ability to control inbound traffic from the ISPs to the data center. What is the most appropriate design consideration for achieving this goal?
- A
Use BGP community attributes to tag routes and apply selective route filtering for inbound traffic control.
- B
Configure BGP with default routes only to simplify routing and minimize control plane overhead.
- C
Implement equal-cost multi-path (ECMP) routing to load-balance inbound traffic from the ISPs.
- D
Use BGP Prepend and MED attributes to influence inbound traffic from the ISPs.
Show answer and explanation
Correct answer: D
Explanation
In a scenario where an enterprise connects to multiple ISPs and wants to control inbound traffic, BGP Prepend and MED attributes are the most appropriate tools. Prepending allows you to make certain paths less preferred by adding your AS number multiple times to the AS path, while MED provides a way to signal preference for specific routes to a particular ISP. This approach ensures stable, secure, and scalable routing in a multi-ISP environment.
- A. Incorrect.
Using BGP community attributes is more suited for outbound traffic control or tagging policies for specific route propagation but does not effectively control inbound traffic from external ISPs.
- B. Incorrect.
Configuring BGP with default routes simplifies routing but provides very limited control over inbound traffic, which is critical in this scenario.
- C. Incorrect.
While ECMP is useful for load-balancing outbound traffic, it is not applicable for inbound traffic control in BGP, especially when dealing with multiple ISPs.
- D. Correct.
BGP Prepend and MED attributes are effective tools for influencing how ISPs route inbound traffic to your network. Prepending increases the AS path length to make a route less preferred, while MED can indicate preferred paths to the ISPs.