How to "silence" a TCP connection in one direction?

Solution 1:

There are a couple of possible ways to do this:

• Try setting a firewall on one of the machines, and blocking the packets from the other side.
• If you cannot install a firewall, try the same as above, with another box (pc with two interfaces, router,...) inbetween, forwarding packets from one side to another, then filter the packets on the box (you can also bridge the two interfaces, and just add filter rules).
• Add a switch inbetween, and put them into same vlan. After heartbeat is working, put one of the ports to another vlan (link state will still be up, but traffic won't go through. If you have ACL support on the switch, you can achieve the same with ACLs.