Hi Victor,
It kinda depends on the design. Both options are possible…you could have two RRs in the same cluster so they’ll have the same cluster ID. You can also have two RRs, one for each cluster so they’ll have a different cluster ID. The second option is probably the most common one, there are some scenarios where you can have reachability issues when you have two RRs with the same cluster ID…maybe something for another lesson 
Rene