Which of the following statements about route redistribution are correct? (Select all that apply.)
Correct Answer: A,B,D
Detailed Explanation: Route redistribution is a technique used in networks where multiple routing protocols are deployed. It allows a router to import routes learned via one routing protocol (for example, OSPF) into another protocol (such as EIGRP or BGP). This is particularly useful when different parts of a network run different routing protocols, or when legacy protocols coexist with newer ones. A. Injecting Routes Across Protocols: Redistribution makes it possible to share routing information between different routing domains. For example, if one part of a network runs OSPF and another part uses EIGRP, a router can redistribute OSPF routes into EIGRP so that both parts of the network have connectivity. This capability ensures that routers using different protocols have a unified view of the network topology. As such, Option A is correct. B. Avoiding Routing Loops: One significant risk when redistributing routes is the creation of routing loops. Redistribution can inadvertently reintroduce routes back into the originating protocol unless measures are taken. Techniques such as route tagging, filtering, and carefully adjusting administrative distances are critical to prevent loops and maintain network stability. Administrators often tag redistributed routes so that they can be identified and selectively filtered in subsequent redistributions. This makes Option B correct. C. Preservation of Routing Metrics: While route redistribution transfers routes between protocols, it does not automatically preserve all metric attributes. In many cases, the metrics from the source protocol are not directly compatible with the destination protocol’s metric system. For instance, converting an OSPF cost into an EIGRP composite metric requires mapping values that may not be a one-to-one conversion. In some configurations, default metrics must be applied during redistribution. Therefore, Option C is incorrect. D. Mixed-Protocol Environments: In large, complex networks—especially those undergoing gradual upgrades or mergers—different routing protocols often coexist. Redistribution is a common technique used to allow these heterogeneous networks to communicate. It is an essential tool for network designers who need to integrate multiple routing domains. This makes Option D correct. Practical Considerations: When configuring redistribution, network engineers must pay careful attention to avoid unintended side effects. Misconfiguration can lead to suboptimal routing decisions or network instability. Best practices include using route maps to control which routes are redistributed, applying route tags for future filtering, and fine-tuning administrative distances to prioritize the most trustworthy routes. Testing changes in a lab environment before deployment in production is recommended. Conclusion: Route redistribution is a powerful tool that enhances network interoperability by allowing different routing protocols to share routing information (Option A) and is especially useful in multi-protocol environments (Option D). However, caution must be exercised to prevent routing loops (Option B), and it is important to understand that metrics are not automatically preserved during redistribution (making Option C incorrect). Mastery of redistribution concepts is essential for troubleshooting and designing scalable, heterogeneous networks.
This CCNA practice question helps students prepare for Cisco networking certification exams by testing knowledge of network fundamentals, routing, switching, and network security concepts.