300-420 Question 124
Select 3You are designing a multi-branch enterprise network where external BGP (eBGP) is used to exchange routes with multiple ISPs. To prevent inadvertent route propagation and ensure network security, which route filtering techniques should you implement?
- A
Use prefix lists to filter specific routes based on IP prefixes.
- B
Implement route maps to apply policy-based filtering for inbound and outbound routes.
- C
Enable route redistribution between eBGP and OSPF without any filters.
- D
Use AS path filtering to restrict routes based on Autonomous System numbers.
- E
Disable route filtering entirely to ensure full connectivity across ISPs.
Show answer and explanation
Correct answers: A, B, D
Explanation
Route filtering is crucial in an enterprise network to ensure security, prevent route leaks, and maintain control over the routing table. Prefix lists, route maps, and AS path filtering are all valid methods to apply control over incoming and outgoing routes. Disabling route filtering or redistributing routes without applying filters can cause significant operational and security issues.
- A. Correct.
Prefix lists are an effective way to filter specific IP prefixes. They allow you to permit or deny specific routes, ensuring only authorized prefixes are advertised or accepted.
- B. Correct.
Route maps provide a flexible mechanism for applying policy-based filtering. They can match on various criteria like prefix lists, AS paths, and more, making them a powerful tool for route control.
- C. Incorrect.
Route redistribution without any filters can lead to route leaks or incorrect propagation of internal routes to external ISPs, which is a bad practice in enterprise network design.
- D. Correct.
AS path filtering allows you to restrict routes based on their Autonomous System numbers, which can prevent routes from specific ASes from being accepted or advertised.
- E. Incorrect.
Disabling route filtering entirely is not recommended as it can lead to security vulnerabilities, route leaks, and propagation of incorrect routes.