A network consists of various remote sites that connect back to two main locations. Pete, the security
administrator, needs to block TELNET access into the network. Which of the following, by default, would
be the BEST choice to accomplish this goal?

A.
Block port 23 on the L2 switch at each remote site

B.
Block port 23 on the network firewall

C.
Block port 25 on the L2 switch at each remote site

D.
Block port 25 on the network firewall

Explanation:
Telnet is a terminal-emulation network application that supports remote connectivity for executing
commands and running applications but doesn’t support transfer of fi les. Telnet uses TCP port 23.
Because it’s a clear text protocol and service, it should be avoided and replaced with SSH.
Incorrect Answers:
A, C: L2 switches may interconnect a small number of devices in a home or the office. They are normally
used for LANs.
D: Port 25 is used by Simple Mail Transfer Protocol (SMTP) for e-mail routing between mail servers.
Stewart, James Michael, CompTIA Security+ Review Guide, Sybex, Indianapolis, 2014, p. 51
http://en.wikipedia.org/wiki/Network_switch#Layer_2
http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers