We are connecting a Dell SonicWall to an AWS TransitGateway, and want to be able to send traffic to multiple VPC CIDRs (subnet ranges).
We have successfully connected the VPN (two green UP tunnels), and can send traffic down the pipe but we get nothing back.
We believe that data is entering the tunnel, and being propagated to the remote VPCs. A box in a VPC appears to be receiving the packet ping and is replying, but the response is being dropped by the VPN.
Traffic is routing across the TG well in all other directions. Network ACLs are permissive. The reply ping is being routed back to the TG Attachment that corresponds to the VPN. There are two tunnels (one is usually failover, but AWS uses both a in all cases anyway), so we have tried both with the Advanced asymmetric tunnel setting on and off.
Essentially, does this sound like the...