Exam AWS Certified Advanced Networking - Specialty ANS-C01 topic 1 question 202 discussion

AWS will route traffic to the data center for addresses within the 172.16.1.0/24 network range using VIF 2 because it provides a more specific route, despite having a longer AS_PATH. Therefore, the correct answer is: B. AWS will route all traffic by using VIF 2.

B is right, here is why AS_PATH Attribute : The AS_PATH attribute of a private IP address indicates the path that packets must take from the internet source to their destination. In this case, both VIFs have an AS_PATH value of 65000. Priority : Since both VIFs have the same AS_PATH value, AWS will use the AS_PATH value of VIF 2 (65000 65000 65000) as a priority for routing traffic to destinations in the 172.16.1.0/24 network range. First Match Wins : When there are multiple paths available from the same source, AWS uses the first match rule that is more specific and has fewer AS_PATH attribute values. In this case, VIF 2 is a subset of VIF 1, so it will be used for routing traffic to destinations in the 172.16.1.0/24 network range.

B is right The AS_PATH attribute value in VIF 1 only includes one value (65000), indicating that the route for 172.16.0.0/16 is directly connected to the data center and not learned from another BGP peer. In contrast, the AS_PATH attribute value in VIF 2 includes three values (65000, 65000, 65000), indicating that the route for 172.16.1.0/24 is learned from another BGP peer with an additional ASN of 65000. Because the route for 172.16.1.0/24 includes an additional ASN, it will be preferred over the route for 172.16.0.0/16 when routing traffic within the data center. Therefore, AWS will route all traffic destined for the 172.16.1.0/24 network range by using VIF 2

B. AWS will route all traffic by using VIF 2. In AWS Direct Connect, traffic is routed based on the most specific route. In this scenario, there are two VIFs advertising routes for different portions of the 172.16.0.0/16 network: VIF 1 advertises the 172.16.0.0/16 network. VIF 2 advertises the more specific subnet 172.16.1.0/24 within the 172.16.0.0/16 network. Since VIF 2 advertises a more specific route (172.16.1.0/24), AWS will prefer this route for traffic destined for the 172.16.1.0/24 network. Therefore, the correct answer is:

B, most specific prefix wins!