In each Terminal, begin roscores individually:

$ initros1
$ roscore

Now, go to the respective multimaster_fkie package folder and run the following command in each computer:

$ rosrun fkie_master_discovery master_discovery _mcast_group:=220.0.0.251

Here, _mcast_group is the multicast IP address we acquired using the netsat command.

If the network was set up properly, you should see the master_discovery node identifying the roscores in each computer, as shown here:

Now, to synchronize between the topics of each ROS master, run the master_sync node in each computer. As we can see, the multimaster_fkie package is set. Let's try the same with an example to understand this better.