If each customer has their own subnet, put them on different vlans. Then, unless pim/RP are configured other customers won't see it. If customers have a single IP in a subnet in the same vlan shared with multiple customers, you probably want to do multicast filtering on the port. Be aware you don't want to filter all multicast as routers & ipv6 also use it (as well as other things that may be of interest to end hosts). Also be aware: Multicast filtering is generally done in switch CPU, so before implementing you may want to see if this is feasible. A more distributed approach may be to filter on the VPS itself.