While connected from home to an ISP (Internet Service Provider), a network administrator performs a port scan against a corporate server and encounters four open TCP (Transmission Control Protocol) ports: 25, 110, 143 and 389. Corporate users in the organization must be able to connect from home, send and receive messages on the Internet, read e-mail by beams of the IMAPv.4 (Internet Message Access Protocol version 4) protocol, and search into a directory services database for user email addresses, and digital certificates. All the e-mail relates services, as well as the directory server, run on the scanned server. Which of the above ports can be filtered out to decrease unnecessary exposure without affecting functionality?
A.
25
B.
110
C.
143
D.
389
Explanation:
Internet message Access Protocol v4 uses port 143 and TCP for connections. POP3 uses port 110 and TCP for connections and therefore can be filtered out to decrease unnecessary exposure.
Reference: Security + (SYBEX) page 130