300-420 Question 138
Select 4An enterprise network is using OSPF as its internal routing protocol and BGP for external connectivity to multiple ISPs. The network administrator needs to redistribute OSPF routes into BGP on the edge routers. Which considerations should the administrator account for when performing this redistribution to avoid potential routing issues?
- A
Ensure that only specific OSPF routes are redistributed into BGP using route maps or prefix lists.
- B
Redistribute all OSPF routes into BGP without any filtering to ensure complete route visibility.
- C
Set proper BGP attributes, such as MED or local preference, to control route selection in the BGP domain.
- D
Avoid redistributing external (Type 5) OSPF routes into BGP to prevent route loops.
- E
Use route summarization during redistribution to reduce the size of the BGP routing table.
Show answer and explanation
Correct answers: A, C, D, E
Explanation
Redistributing OSPF routes into BGP requires careful planning to prevent routing loops, excessive route propagation, and scalability issues. Filtering specific routes, avoiding the redistribution of external OSPF routes, and applying summarization are best practices to mitigate these risks. Additionally, using BGP attributes ensures proper route selection and traffic control within a BGP domain.
- A. Correct.
Filtering specific OSPF routes ensures that only necessary routes are advertised into BGP, preventing unnecessary route propagation and potential routing loops.
- B. Incorrect.
Redistributing all OSPF routes without filtering can lead to excessive and unintended route advertisements, increasing the risk of routing instability.
- C. Correct.
Setting proper BGP attributes helps control route preference and ensures that BGP makes optimal routing decisions when considering redistributed OSPF routes.
- D. Correct.
Avoiding redistribution of external OSPF routes (Type 5) into BGP prevents potential routing loops, especially when these routes originate from another autonomous system.
- E. Correct.
Summarizing routes during redistribution reduces the size of the BGP routing table, improving scalability and performance while minimizing unnecessary route churn.