Common Ports

Question 1

What is Telnet? What port does it use? What is a downside?

Answer 1

Telecommunication Network. TCP Port 23. A way to login to devices remotely, and controlled through a text based console. It’s a way to connect to infrastructure devices (server/router/switches) to administrate those machines.
A downside is that it is sent non-encrypted, so it is not the best choice for production systems.

Question 2

What is SSH? What port does it use? How is it compared to Telnet?

Answer 2

SSH is Secure Shell. TCP Port 22. Works the same as Telnet but sends encrypted communications.

Question 3

What is DNS? What port does it use?

Answer 3

Domain Name System. UDP Port 53. DNS converts domain names that we use to something that the network can use, like an IP addresses.
Example: www.professormesser.com = 162.159.246.164

Question 4

What is SMTP? What port does it use?

Answer 4

Simple Mail Transfer Protocol. TCP Port 25. Sends mail from one server to another. Commonly configured on mobile devices and email clients.

Question 5

What are some common protocols that are used for incoming mail?

Answer 5

IMAP, POP3.

Question 6

What is SFTP? What port does it use? What protocol does it utilize? What can it do?

Answer 6

Secure File Transfer Protocol. TCP Port 22. Utilizes the SSH (Secure Shell) File Transfer Protocol. It can transfer files remotely, resume interrupted transfers, directory listings, and remotely remove files. This is all encrypted.

Question 7

What is FTP? Which two ports does it use and why? How does it differ from SFTP? What kind of features does it have?

Answer 7

File Transfer Protocol. TCP Port 20 (Active mode data protocol). TCP Port 21 (Control protocol). Transfers files between systems. Requires authentication with a username and password. Has a list of features, such as list/add/delete.

Question 8

What is TFTP? What port does it use? Why would you use TFTP?

Answer 8

Trivial File Transfer Protocol. UDP Port 69. Could be used for very simple file transfers, as it doesn’t require any authentication or encryption.

Question 9

What is DHCP? What ports does it use to communicate? What does it require?

Answer 9

Dynamic Host Configuration Protocol. UDP Port 67 and 68. It automatically configures your IP address, subnet mask, DNS settings, within your IP Config. It requires a DHCP Server.

Question 10

How are DHCP IP addresses assigned? How does it work?

Answer 10

IP addresses are assigned in real-time from a pool of IP addresses. Each system is given a lease, and must renew at set intervals.

Question 11

What is DHCP Reservation?

Answer 11

When you configure DHCP to always give the same devices the same MAC address.

Question 12

What is HTTP? What port does it use? What is it for?

Answer 12

Hypertext Transfer Protocol. TCP Port 80. Web server communication. Commonly used by browsers.

Question 13

What is HTTPS? What port does it use? What is it for?

Answer 13

Hypertext Transfer Protocol Secure. TCP Port 443. Web server communication with encryption. Commonly used by browsers.

Question 14

What is SNMP? What port does it use?

Answer 14

Simple Network Management Protocol. UDP Port 161. Used to gather data/statistics from network devices.

Question 15

Name the versions of SNMP, and the features of each.

Answer 15

v1 - structured tables, sent requests/responses non encrypted.
v2 - allowed bulk transfers of data. Also non-encrypted.
v3 - message integrity, authentication, and encryption.

Question 16

What is RDP? What port does it use?

Answer 16

Remote Desktop Protocol. TCP Port 3389. Allows to connect to another desktop or application remotely to share control.

Question 17

What is NTP? What port does it use?

Answer 17

Network Time Protocol. UDP Port 123. Used by switches, routers, firewalls, servers, and workstations to synchronize to the same date and time. Administrator can control how often NTP is utilized to synchronize the network’s time.

Question 18

What is SIP? What ports does it use?

Answer 18

Session Initiation Protocol. TCP Port 5060 and 5061. Used for VoIP signalling. Setup and manage VoIP sessions. Extend voice communications.

Question 19

What is SMB? What port does it use?

Answer 19

Server Message Block AKA CIFS (Common Internet File System). Uses TCP Port 445. Used for file sharing, and to share printers between windows systems.

Question 20

What is the basic function of POP and IMAP?

Answer 20

To receive emails from an email server; authenticate and transfer.

Question 21

What is POP? What port does it use?

Answer 21

POP3 - Post office Protocol version 3. TCP Port 110. This is a basic mail transfer functionality.

Question 22

What is IMAP? What port does it use?

Answer 22

IMAP4 - Internet Message Access Protocol v4. TCP Port 143. This allows us to use multiple clients to access our inbox.

Question 23

What is LDAP? What port does it use?

Answer 23

Lightweight Directory Access Protocol. TCP Port 389. Users’ devices and printers are usually stored in a database. This is accessed via LDAP. LDAP allows our client to communicate to an LDAP server AKA retrieve information in a network directory.

Question 24

What is LDAPS? What port does it use?

Answer 24

LDAP Secure. TCP Port 636. Same as LDAP but encrypted by SSL.

Question 25

What is H.323 and what is it similar to? What port does it use?

Answer 25

Also used for VoIP, similar to SIP. TCP Port 1720. Allows us to setup and manage VoIP sessions.