The below steps are to network administrator of an upper-tier ISP can implement policy when configuring BGP:
Let us assume Assumethe three ISPs such as ISP A, ISP B and ISP C.
Take ISP B does not carry between ISP A and ISP C.
Then ISP A and ISP C have ISP B as their BGP peers
ISP B does not promote to ISP A, which authorization through ISP C.