[Problem] No SYN,ACK in TCP 3-ways handshake

[Problem]

A Client can not receive SYN,ACK packet from A Remote Server even though it can successfully do PINGs between them.

Environment: Customized Mininet Topology 

 

[Check Point]

1. Capture TCP packets on a virtual ethernet.

2. The port is open or not

3. Firewall in a host is working or not