This document provides an introduction to common ports and protocols. It discusses how ports specify the protocol or service being accessed and can be thought of as extensions, while protocols are the languages that applications use to communicate. It then lists and describes several common protocols and their assigned ports, including FTP (20-21), SMTP (25), HTTP (80), DNS (53), and SSH (22).

1. Common ports
and protocols.

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Instructor, PACE-IT Program – Edmonds Community College
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 PC Hardware
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 B.S., IT Security, Western Governor’s University
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– Introduction to ports and protocols.
– Some common ports and protocols.
PACE-IT.

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Common ports and protocols.

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– Ports.
» A method of specifying what protocol or service to access.
• Protocol and services use default ports so they are easy to locate.
» There are 65,536 ports available to be used for communication, but
port 0 is reserved. So, in actuality, only ports 1 to 65,535 are
available.
• The first 1024 ports are specifically assigned and are called well
known ports.
• www.iana.org/assignments/port-numbers.
» They can also be thought of as phone number extensions.
• The IP address is the main number you are trying to reach.
• The port is the is the extension (service or protocol) you want to
access.
– Protocols.
» Extending the telephone analogy, protocols can be thought of as
the language that the two applications on either side of the
connection agree to speak.
» Protocols translate requests into services.
» Most protocols use defined ports, but some protocols must be user
configured.
Common ports and protocols.

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Ports are not protocols and
protocols are not ports.
Even though the two are closely associated they are
not the same. Ports are used to request (access)
services or applications. Protocols are the services or
applications that are being requested.
When a requestor seeks to connect to a specific port,
the requestor is dynamically assigned a port number
to “listen to” for the response. This also allows for
computers to have many concurrent connections.
Common ports and protocols.

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Common ports and protocols.

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– FTP (File Transfer Protocol).
» A standard protocol for transferring files between computing
systems.
• Assigned to port 20 and to port 21 (mostly uses port 20).
– SFTP (Secure File Transfer Protocol).
» An encrypted version of FTP, which uses Secure Shell (SSH).
• Assigned to port 22.
– SMTP (Simple Mail Transfer Protocol).
» The protocol used to transfer email from a client to an email
server; it is also used to transfer email between servers.
• Assigned to port 25.
– POP3 (Post Office Protocol v3).
» The protocol used by clients to retrieve email from servers.
• Assigned to port 110.
Common ports and protocols.

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– IMAP (Internet Message Access Protocol).
» A protocol used by clients to access email on email servers.
Allows the client to organize email on the server into folders.
• Assigned to port 143.
– HTTP (Hypertext Transfer Protocol).
» The primary protocol used to transfer data over the Internet.
• Assigned to port 80.
– HTTPS (Hypertext Transfer Protocol
Secure).
» The primary protocol to securely transfer data over the Internet
using SSL (Secure Socket Layer) or TLS (Transfer Layer
Security) technology. In actuality, SSL should no longer be
used.
• Assigned to port 443.
Common ports and protocols.

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– DNS (Domain Name System).
» The protocol that is used to map computer names to their IP
addresses (e.g., www.google.com to 74.125.28.104).
• Assigned to port 53.
– RDP (Remote Desktop Protocol).
» Used in Microsoft networks by Remote Desktop Connection
and Remote Assistance to make remote connections.
• Assigned to port 3389.
– DHCP (Dynamic Host Configuration
Protocol).
» The protocol used within networks to automatically configure
computers with the correct IP configurations (e.g., IP address,
subnet mask, default gateway, and DNS server location).
• The DHCP server is assigned to port 67.
• The requesting client listens for the response on port 68.
Common ports and protocols.

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– LDAP (Lightweight Directory Access
Protocol).
» The protocol used for accessing and maintaining distributed
directory information services (e.g., Active Directory Domain
Services).
• Assigned to port 389.
– SNMP (Simple Network Management
Protocol).
» A protocol used to monitor and manage local area networks.
• Assigned to port 161.
– SMB (Server Message Block).
» A protocol used to transfer files over a network; the process is
transparent to the user.
• Assigned to port 445.
Common ports and protocols.

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– CIFS (Common Internet File System).
» A protocol used to share files across intranets (internal private
networks) and the Internet.
• Assigned to port 3020.
– SSH (Secure Shell)
» A protocol used to encrypt data traffic on a network.
• Assigned to port 22.
– Telnet.
» A protocol used for remote access to systems; it is unsecure. It
is a bi-directional terminal service.
• Assigned to port 23.
Common ports and protocols.

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Common ports and protocols.
Ports are a method of specifying what protocol or service a requestor is
seeking access to. They can be thought of as being the specific location of
that protocol or service. Protocols translate the request into a specific
service. Of the possible 65,536 ports, 1024 ports are well known (clearly
defined as to their purpose). Most protocols are automatically assigned to
ports; however, some must have their ports configured by the user.
Topic
Introduction to ports and
protocols.
Summary
FTP (20 and 21), SFTP (22), SMTP (25), POP3 (110), IMAP (143), HTTP
(80), HTTPS (443), DNS (53), RDP (3389), DHCP (67 and 68), LDAP
(389), SNMP (161), SMB (445), CIFS (3020), SSH (22), and Telnet (23).
Some common ports and
protocols.

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