Can a router select another router to join ?

I use S2c…You say NJ0 to select the specific parent of end device.
I know mesh policy for your xbee module…
There are C-R1-R2-E… I think R2 will connect both R1 and C.
R2 is near R1…
But when I read the routing information of R2 using the ZDO command 8032,
I found the cordinator in it…
If the router policy mesh policy…
it’s routing information shows both the route1( R2-C) and the route2(R2-R1)
I don’t understand the situation…
So I tried your NJ policy…
After I joined R1 to C, I did NJ0 in C.
So I expeceted that R2 would connect R1…
R1’s routing information include R2…
But R2’s routing informatin didn’t include R1-R2. only R2-C.

NJ0 is usable for end device’s parent selection?

NJ does not control routing. It controls who is the parent of a device only. For end device communications, All data must flow between the parent and the end device. Then get routed to the destination with the least amount of hops possible. So if you have C1, R1, R2 and E1, if E1 is connected to R2, and if R2 and R1 are both in range of the Coordinator (C1), R2 will as a parent of E1 will send the data directly to the Coordinator. Now if R2 is out of range of the Coordinator but in range of R1 and R1 is in range of the Coordinator, then the data will flow through R1.