An important control that should be in place for external connections to
a network that uses call-back schemes is:

A.
Call enhancement

B.
Breaking of a dial-up connection at the organization’s computing
resource side of the line

C.
Breaking of a dial-up connection at the remote user’s side of the line

D.
Call forwarding

Explanation:
One attack that can be applied when call back is used for remote,
dial-up connections is that the caller may not hang up. If the caller
had been previously authenticated and has completed his/her session,
a live connection into the remote network will still be maintained.
Also, an unauthenticated remote user may hold the line open,
acting as if call-back authentication has taken place. Thus, an active
disconnect should be effected at the computing resource’s side of the
line.
Answer “Breaking of a dial-up connection at the remote user’s side of the line” is not correct since
it involves the caller hanging up.
Answer “call forwarding” is a feature that should be disabled, if possible,
when used with call-back schemes. With call back, a cracker can

have a call forwarded from a valid phone number to an invalid
phone number during the call-back process. Answer “Call enhancement” is a distracter.