In this example, the client send a ping to 172.25.100.2 (the interface B of the server through interface A).
By default Redhat/CentOS 7 don't respond to a ping coming from an other interface than the one who is asked, no reply is returned from the server
A TCPdump can show you the server receive the request but do not send a single reply.
The solution is simple.
echo 2 > /proc/sys/net/ipv4/conf/all/rp_filter