When ‘B’ initiates a connection to the remote site. It dials an external modem on a serial port, or an internal modem (which thinks it is a serial port). The end of that process to enable telnet is the acknowledgement of an interrupt (hardware even if wirtualized). Every time I have seen this sort of problem (and it is still prevalent) the secondary machine “A” requests a tcp/ip connection to the remote site from “B”, and ‘B’ looks at the routing table gives ‘A’ the last valid IP address and stops, never having dialed the remote site. Or having dialed the remoste site never passes the new IP address back to ‘A’.
It is a place to start – Good Luck.