Exam AWS Certified Advanced Networking - Specialty ANS-C01 topic 1 question 48 discussion

B - correct. Option B is the correct solution. Set the BGP community tag for all prefixes from the primary data center to 7224:7300, and set the BGP community tag for all prefixes from the failover data center to 7224:7100. This way, the primary data center will have a lower BGP local preference, making it the preferred path. If there is an outage in the primary data center, the failover data center will have a higher BGP local preference and will become the preferred path. The other options do not provide the correct community tag values for the primary and failover data centers.

Correct answer is B. TGW + DxGW (transit VIF), so the BGP community tags in use are 7224:7100/7200/7300, with 7300 is the highest priority and takes precedence, therefore to be used with primary DC.

B is the correct answer 7224:7300 has the highest priority whilst 7224:7100 has the lowest ( 7224:7X BGP communities are used for private/transit vifs) A is wrong since the priority is wrong whilst the correct tag 7X00 were used C&D are since the 7224:9X BGP communities are used for public vifs

BGP community tags are used to influence routing decisions. In this case, the tags are set differently for the primary and failover data centers. Setting the BGP community tag for all prefixes from the primary data center to 7224:7300 indicates a preference for routing through the primary data center. Setting the BGP community tag for all prefixes from the failover data center to 7224:7100 indicates that this is a failover route and should only be used in the case of an outage. This configuration ensures that traffic is routed to the primary data center by default and only fails over to the secondary data center in case of an outage in the primary data center.

C & D: are using 7224:9XX which are for Public VIFs

https://repost.aws/knowledge-center/direct-connect-bgp-communities Direct Connect supports local preference BGP community tags to control the route preference of traffic on private and transit virtual interfaces. Direct Connect supports the following local preference BGP communities: 7224:7100 Low preference, 7224:7200 Medium preference, and 7224:7300 High preference1. Direct Connect evaluates local preference BGP community tags from lowest to highest preference. For each prefix that you advertise over a BGP session, you can apply a community tag to indicate the associated path’s priority for returning traffic1.

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See section "Local preference BGP communities" from: https://docs.aws.amazon.com/directconnect/latest/UserGuide/routing-and-bgp.html

It is B)

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