route priority question about DX

Question

hi, All

Customer is try to change from Private VIF direct attach to VGW to direct connect gateway. The question is:
during the operation, one VIF will attach to VGW and the other VIF will attache to DX-GW. This VGW is also associated with the DX-GW.

How VGW decide the route priority from connected VIF and DX-GW. Will the "as-path" or "community" still work?

Thanks

Accepted Answer

Assuming both DX connections are in same co-lo, then:

VGW: VIF would be preferred over DXGW:VIF for return path (assuming both sessions are advertising same prefixes). You can use AS PATH prepending or LP commnities to control ingress traffic from AWS.

The recommended way to control ingress traffic from AWS going to a VPC is by using LP communities or AS PATH Prepending https://docs.aws.amazon.com/directconnect/latest/UserGuide/routing-and-bgp.html

Again, this is pretty tricky, "we set localpref for local region VIFs so that will override the AS prepend from remote region VIFs in some cases." This things also varies when 2 DX connections are from different co-locations homing same AWS region. Hence, it is recommended to get complete control to the ingress traffic flow through LP communities.

route priority question about DX

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