在PIM域A内的一个组播客户希望接收到一个在PIM域B内的组播源。在每个域内的 RP之间建立MSDP的session。在SA发送前,哪一种转发树生成?()
A. An RPT from the DR to the RP in domain A
B. An RPT from the DR to the RP in domain B
C. An SPT from the RP in domain A to the first-hop router
D. An SPT from the RP in domain B to the first-hop router
E. An SPT from the DR to the first-hop router