300-420 Question 216
Single answerAn enterprise network is connected to two different ISPs for redundancy and improved availability. The network administrator wants to ensure that outbound traffic is distributed between the two ISPs based on the prefix-specific routing policies while maintaining failover capabilities. Which approach best addresses this requirement?
- A
Use static routing with equal-cost routes to both ISPs.
- B
Implement Border Gateway Protocol (BGP) with a single Autonomous System (AS) and configure prefix-based route filtering.
- C
Configure Policy-Based Routing (PBR) to manually direct traffic to each ISP.
- D
Enable BGP with two different Autonomous Systems (AS) and configure AS-Path prepending for failover.
Show answer and explanation
Correct answer: B
Explanation
In a multihomed environment, BGP is the preferred protocol for managing traffic distribution and failover. Configuring BGP with a single Autonomous System (AS) allows the enterprise to maintain control over traffic leaving the network. By implementing prefix-based route filtering, the administrator can control how traffic is distributed between the ISPs while ensuring redundancy and failover capabilities. This approach is both scalable and efficient for enterprise networks.
- A. Incorrect.
Static routing with equal-cost routes does not allow for advanced traffic engineering or prefix-based control. Additionally, static routing lacks the dynamic failover capabilities provided by BGP.
- B. Correct.
Implementing BGP with a single Autonomous System (AS) and prefix-based route filtering allows precise control over outbound traffic distribution and ensures dynamic failover. This is a standard and scalable approach for multihomed enterprise networks.
- C. Incorrect.
Policy-Based Routing (PBR) can manually direct traffic, but it is not scalable for large networks or dynamic failover scenarios. It also lacks the flexibility of BGP for prefix-specific routing.
- D. Incorrect.
Using BGP with two different Autonomous Systems (AS) and AS-Path prepending is typically used for inbound traffic manipulation rather than outbound traffic control. It does not provide the level of control needed for outbound traffic distribution based on prefixes.