In a Carrier Supporting Carrier (CSC) VPRN model, the ingress backbone provider edge router (PE1) receives packets from the customer carrier's edge router (CSC-CE1) that are already MPLS-labeled. CSC-CE1 applies the customer's own VPN label before forwarding the packet to PE1. PE1 then pushes two additional labels onto this already-labeled packet: a BGP/VPN label for the backbone VPRN to reach the egress PE (PE2) and a transport label (e.g., LDP) to traverse the backbone core. Therefore, the statement that PE1 pushes two labels onto the "IP packet" is false; it pushes them onto a labeled packet, resulting in a three-label stack.

A. CE1 forwards the data packet to PE1 via the VPRN 20 interface.

This statement is correct. The packet travels from CE1 to CSC-CE1, which then forwards it to PE1 over the access interface assigned to the backbone carrier's VPRN 20.

C. CSC-CE1 pops the LDP label and swaps the BGP label.

This statement is incorrect