Multicast - How a source joings a MC group?

[fjcardenas-1]

I am a bit confused with Multicast. I know receivers that want to join a specific multicast group use IGMP to request to join to the group (lets say 239.4.1.1). My question is on the source side. Does the source also use IGMP to join the group? Or how does the source join the multicast group? If anyone has an example would be appreciated. Thank you.

[Joseph W. Doherty]

Multicast sources don't join a multicast group, they just transmit. A multicast router, will "see" the multicast stream (if on a connected router interface) and then will redistribute, by the rules of the multicast routing protocol being used.

[rais]

To add to Joseph's explanation, for PIM specifics are:

https://www.juniper.net/documentation/en_US/junos/topics/concept/multicast-pim-sparse-mode-registration.html

and

https://tools.ietf.org/html/rfc7761#section-3.1 + section 3.2

Thanks.