I have a device “X” with the IP as 192.168.0.5, Subnet mask – 255.255.255.0 which is set to send the UDP multicast frames at the multicast IP – 239.0.0.0, destination port – 5001 I am directly connecting my laptop to this device – Laptop IP is 192.168.0.100 First, I do not see any multicast frames at all; I am using wireshark to monitor the network. There is no switch in between – Just my laptop running wireshark and the device “X”. Then, when I define a Gateway address in the “X”, say 192.168.0.24 – I started seeing the UDP multicast frames on the wireshark. My question is: Why is it required to define a gateway in the device “X”? Shall it not simply send the multicast UDP frames out of the port defining the multicast destination address as UDP does not require a connection to be established before the flow of data? Also, the below frames do not mention any Gateway address, then what is the reason that the device “X’ is dependent on the gateway address:
![Wireshark Frame][1] Is there a problem with the implementation of multicast UDP in the device? The below questions are about the Multicast TCP/UDP Frames: 1. Since my PC is not a part of the multicast group (239.0.0.0), it shall not see any frames which are destined for 239.0.0.0 – then why do I see the frames on wireshark? Is it because there is no mechanism to filter those frames? And if I use a switch with IGMP, I’d not see those multicast frames if my PC is not a part of 239.0.0.0? 2. I read that the multicast IP is mapped to the layer-2 Multicast MAC. Also, I can see from the above wireshark frames that there is an IPv4_multicast MAC. Question is: How can I see a list of MAC addresses that my PC is going to accept and forward to the upper layers? Thank you for your answers.
Can't post wireshark image as I don't have the reputation :(
