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I am able to find multicast groups by using this in Command Prompt (I found this at serverfault How do I know if IP Multicasting is enabled on my network in Windows?).

netsh interface ip show joins

Here is the result:

Scope       References  Last  Address
----------  ----------  ----  ---------------------------------
0                    0  Yes   213.0.0.1
0                    1  Yes   213.0.0.23

I am able to use 213.0.0.23 for the multicast IP address to send/receive data. My question is how I can find the number of members in a multicast group?

Thanks!

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curious1
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    You will need to use IGMP to discover which hosts are subscribed to multicast groups. By the way, `213.0.0.23` is not a valid multicast address. You send from a regular IP address to a multicast address. The multicast address range is `224.0.0.0/4`, but some addresses are reserved for special purposes (e.g. `224.0.0.1` is the all-hosts multicast group). In general, you should use multicast groups in the administratively scoped range (`239.0.0.0/8`). – Ron Maupin Apr 02 '16 at 23:13
  • Ron, 213.0.0.23 is what I made up to protect our system. I have a few Windows virtual servers (2012 R2 Standard). Do you have a pointer for install/configure IGMP on servers? – curious1 Apr 03 '16 at 00:54
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    You don't need to make up multicast group numbers since they cannot be routed on the Internet. All hosts have IGMP enabled. You should learn how IGMP works: [RFC 3376](https://tools.ietf.org/html/rfc3376) and [RFC 4605](https://tools.ietf.org/html/rfc3376). There may be tools to help with this, but "_product, service, or learning material recommendations_" are explicitly off-topic here. – Ron Maupin Apr 03 '16 at 01:00
  • Ron. Our servers run on the same internal network (not on the internet). We use multicast for Tomcat clustering. Is multicast a good solution in our case? Thanks for your info. Voted up your answers. – curious1 Apr 03 '16 at 01:29
  • I can't answer that question. I plead application ignorance; I'm a network guy. – Ron Maupin Apr 03 '16 at 02:08

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