How to join multicast group on specific interface

Hello, I need to join a MC group lets say port 21000

and I need to join on a local interface with IP of

I want to test to see if Im recieving any data from the group

looking at docs, how do I specify the MC port 21000 ?

also, do I bind to my local 192.168 address? ie, bind(socket, ip"", 6789) ?

using Sockets
group = ip""
socket = Sockets.UDPSocket()
bind(socket, ip"", 6789)
join_multicast_group(socket, group)
leave_multicast_group(socket, group)