Based on the diagram you have provided, you've told hosts in the 10.12.0.0/24 network now to reach hosts in the 172.30.0.0/16 network. but you haven't done the same for the opposite. Therefore, if you ran a capture on the port going to 172.30.1.1, you should be able to see the Echo requests going towards host B, but the Echo replies not being returned.