Source and destination addresses of targeted Hello packets are the LDP LSR-IDs of systems A and B.
The user can configure the local-lsr-id option on the targeted session and change the value of the LSR-ID to either the local interface or to some other interface name, loopback or not. If the local interface is selected the IP address of the local interface will be used as the LSR-ID. In all cases, the transport address for the LDP session and the source IP address of targeted Hello message will be updated to the new LSR-ID value.
The LSR with the highest transport address, that is, LSR-ID in this case, will bootstrap the TCP connection and LDP session.
Source and destination IP addresses of LDP messages are the transport addresses, which, in this case, are the LDP LSR-IDs of systems A and B.