An oil & gas company has set up a dynamic VPN link to AWS VGW for accessing web applications deployed in AWS VPC. They have commissionedAWS Direct Connect to AWS VGW from the customer`s end Cisco router for higher bandwidth requirements. When the server team was trying to reach servers in VPC Private subnet, they found that the traffic is flowing through the VPN link, not through the Direct Connect Link and impacting the performance. As a Network Engineer, you found that the prefixes with the same prefix length have been advertised for both the VPN & AWS Direct Connect links. What additional check would you do to prefer AWS Direct Connect?

Answer options:

A.Modify BGP weight lower for VPN Links so that AWS Direct Connect links are preferred.
B.Modify BGP ASN for both VPN & AWS Direct Connect links.
C.Add AS Path Prepend to VPN Links so that the AWS Direct Connect link is preferred.
D.Modify BGP Local Preference to higher values for VPN links so that the AWS Direct Connect link is preferred.

Correct Answer – A
Weight Attribute is local to router & higher weight is preferred. In the above case, since both VPN links & AWS Direct Connect links are terminating on the same router & the same prefixes are advertised to both links, it will prefer AWS Direct Connect links. VPN Link will prefer only if f weight on VPN links is higher than AWS Direct Connect Links. To prefer AWS Direct Connect links for outbound traffic, the weight attribute can be modified so that VPN links have a lower weight than AWS Direct Connect links. With lower weight on VPN links, these links will be back up links & traffic will be flowing out on these links only if AWS Direct Connect links are down.
Option B is incorrect as having a Different ASN for VPN& AWS Direct Connect links is not required.
Option C is incorrect as the addition of AS Prepend will impact incoming traffic & not outgoing traffic.
Option D is incorrect as adding Local Preference higher for VPN links will prefer these links & not AWS Direct Connect links.
Reference:
https://docs.aws.amazon.com/vpn/latest/s2svpn/s2s-vpn-user-guide.pdf#VPC_VPN
https://docs.aws.amazon.com/directconnect/latest/UserGuide/dc-ug.pdf