2 cissp ® Official Study Guide Eighth Edition

Common Application Layer Protocols
In the Application layer of the TCP/IP model (which includes the Session, Presentation, and 
Application layers of the OSI model) reside numerous application- or service-specific proto-
cols. A basic knowledge of these protocols and their relevant service ports is important for 
the CISSP exam:
Telnet
, TCP Port 23
This is a terminal emulation network application that supports 
remote connectivity for executing commands and running applications but does not sup-
port transfer of files.
File Transfer Protocol (FTP)
, TCP Ports 20 (Passive Data)/Ephemeral (Active Data) and 21 
(Control Connection)
This is a network application that supports an exchange of files that 
requires anonymous or specific authentication.
Trivial File Transfer Protocol (TFTP)
, UDP Port 69
This is a network application that 
supports an exchange of files that does not require authentication.
Simple Mail Transfer Protocol (SMTP)
, TCP Port 25
This is a protocol used to transmit 
email messages from a client to an email server and from one email server to another.
Post Office Protocol (POP3)
, TCP Port 110
This is a protocol used to pull email messages 
from an inbox on an email server down to an email client.
Internet Message Access Protocol (IMAP)
, TCP Port 143
This is a protocol used to pull 
email messages from an inbox on an email server down to an email client. IMAP is more 
secure than POP3 and offers the ability to pull headers down from the email server as well 
as to delete messages directly off the email server without having to download to the local 
client first.
Dynamic Host Configuration Protocol (DHCP)