Multiple hosts's IP need to be set the same subnet when communicating each other?

[liyingzhi]

System info:

• A host: ubuntu 16.04
• B host: windows 7
• A and B are connected by a switch.

Test1:

• A host IP : 160.69.69.69
• B host IP: 192.168.151.79

1. The talker at A host multicasts a message named 'EXAMPLE' to the network. The listeners at A and B host both receive the message and enter the handle function.

2. The talker at B host multicasts a message named 'EXAMPLE' to the network. The listener at B host can receive the message and enter the handle function. But the listener at A host never enter the handle function. Then i use Wireshark to monitor the network data at A host, the message from B host can be obtained by A host.

Test2:

• A host IP : 192.168.151.167
• B host IP: 192.168.151.79

1. The talker at A host multicasts a message named 'EXAMPLE' to the network. The listeners at A and B host both receive the message and enter the handle function.

2. The talker at B host multicasts a message named 'EXAMPLE' to the network. The listeners at A and B host both receive the message and enter the handle function.
   The situation at Test1_2 does not happen!

Is there a problem with my A host configuration? Or multiple hosts's IP need to be set the same subnet when communicating each other?

Thank you and looking forward to your reply.

Codes:

• LCM data type defination

package lcm_std_msgs;
struct Header
{
int32_t seq;
int64_t stamp;
string frame_id;
}

• talker:

#include<windows.h>
#include<iostream>
#include<stdio.h>
#include <lcm/lcm-cpp.hpp>
#include "lcm_std_msgs/Header.hpp"
int main(int argc, char **argv)
{
    int i;
    lcm::LCM lcm("udpm://239.1.1.255:7667?ttl=1");
    if (!lcm.good())
        return 1;
    lcm_std_msgs::Header my_data;
    my_data.seq = 1;
    my_data.stamp = 2;
    my_data.frame_id = "OK";
    for(i = 0;i <5; ++i)
    {
        lcm.publish("EXAMPLE", &my_data);
        Sleep(1);
    }
    return 0;
}

• listener:

#include <stdio.h>
#include <iostream>
#include "lcm_std_msgs/Header.hpp"
#include <lcm/lcm-cpp.hpp>

using namespace std;

class Handler {
public:
	~Handler() {}
	void handleMessage(const lcm::ReceiveBuffer *rbuf, const std::string &chan,
		const lcm_std_msgs::Header *msg)
	{
		int i;
		printf("Received message on channel \"%s\":\n", chan.c_str());
		printf("  timestamp   = %lld\n", (long long)msg->seq);
		printf("  position    = (%f, %f, %f)\n", msg->stamp);
		cout << msg->frame_id << endl;
	}
};

int main(int argc, char *argv[])
{
	string address = "udpm://239.1.1.255:7667?ttl=1";
	int i;
	lcm::LCM  lcm(address) ;
	if (!lcm.good())
		return 1;
	Handler handlerObject;
	lcm.subscribe("EXAMPLE", &Handler::handleMessage, &handlerObject);

	while (0 == lcm.handle()) {
		// Do nothing
	}

	return 0;
}

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