DNS load balancing

I have datacenter A and datacenter B. In datacenter A, I have BIG-IP DNS-A and server-A. In datacenter B, I have BIG-IP DNS-B and server-B. BIG-IP DNS are configured with IP anycast that users are routed to the nearest DNS. I want to create a pool on BIG-IP DNS that BIG-IP DNS-A will prefer server-A while BIG-IP DNS-B will prefer server-B.

I know that there is topology load balancing but it needs to define the source request. However, I need to define 2000 CIDR in that case. Is there any simpler to achieve the load balanacing?

Thanks in advance.