ANS-C01 · Question #242
A company has two data centers that are interconnected with multiple redundant links from different suppliers. The company Uses IP addresses that are within the 172.16,0.0/16 CIDR block. The company…
The correct answer is B. Tag the BGP announcements with the local preference BGP community tags. Set the tag to high. Explanation Option B is correct because AWS Direct Connect supports BGP community tags that allow customers to influence routing preferences. By applying a high local preference community tag (e.g., 7224:7300 for highest preference) to routes advertised from the first data…
Question
A company has two data centers that are interconnected with multiple redundant links from different suppliers. The company Uses IP addresses that are within the 172.16,0.0/16 CIDR block. The company is running iBGP between the two data centers by using a private Autonomous System Number (ASN) and IGP. The company is moving toward a hybrid setup in which the company will initially use one VPC in the AWS Cloud. An AWS Direct Connect connection runs from the first data center to a Direct Connect gateway by using a private VIF. On the connection, the company advertises a summarized route for the 172.16.0.0/16 network. The company is planning to set up a second summarized route from the second data center to a different Direct Connect location. The company needs to implement a solution to route traffic to and from AWS through the first Direct Connect connection. The solution must use the second Direct Connect connection for failover purposes only. Which solution will meet these requirements?
Options
- APrepend the private ASN on the BGP announcements to AWS from the second data center. Add
- BTag the BGP announcements with the local preference BGP community tags. Set the tag to high
- CConfigure the Direct Connect gateway to prefer routing through the Direct Connect connection
- DConfigure the focal AWS Region BGP community tag on the BGP route that is advertised from
How the community answered
(31 responses)- A10% (3)
- B74% (23)
- C3% (1)
- D13% (4)
Explanation
Explanation
Option B is correct because AWS Direct Connect supports BGP community tags that allow customers to influence routing preferences. By applying a high local preference community tag (e.g., 7224:7300 for highest preference) to routes advertised from the first data center and a low local preference tag (e.g., 7224:7100) to routes from the second, AWS will consistently prefer the first connection for inbound traffic, using the second only when the first fails.
Option A is wrong because AS path prepending affects outbound routing from AWS (how AWS reaches you), but AS path prepending on announcements to AWS influences inbound traffic - however, this is a valid technique for on-premises routing preference, not the AWS-preferred method for this scenario. More importantly, AS path prepending controls the length of the path, while local preference community tags are the AWS-recommended, purpose-built mechanism for influencing routing priority on Direct Connect.
Option C is wrong because the Direct Connect gateway itself does not have a configurable routing preference setting - routing decisions are controlled via BGP attributes, not gateway configuration.
Option D is wrong because the local AWS Region BGP community tag influences which AWS Region traffic is routed to, not which Direct Connect connection is preferred for primary vs. failover.
Memory Tip: Think of BGP community tags as "priority stickers" - AWS reads these stickers to decide which Direct Connect connection gets the traffic first. High tag = primary, Low tag = failover.
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