Common Network Ports( Comptia Objective 2.1)

Question 1

What is port TCP 20/21 used for?

Answer 1

It is used to handle FTP( File Transfer Protocol). Which transfers files between systems

• TCP/20 used used for active mode data while
• TCP/21 is used for control of the communication
• Has security built in( authenticates with username/password)
• Full featured functionality( list, add, delete, etc)

Question 2

What is port TCP/22 used for?

Answer 2

This is used for SSH( Secure Shell) 
 - Is an Encrypted communication link
 - Used to login remotely to a device
 - Looks like a console command line similar to Telnet
however Telnet is not encrypted.

Question 3

What is port TCP/23 used for?

Answer 3

This is used for Telnet - Telecommunication Netwrok

• TCP/23
• Used to login remotely to a device
• It is In-The-Clear communication and is not encrypted like SSH, not secure at all
• Not commonly used for productive systems.

Question 4

What is port TCP/25 used for

Answer 4

This is used for SMTP - Simple Mail Transfer Protocol

• Used for sending emails Server to server email transfer
• TCP/25
• Also used to send mail from device to a mail server/commonly configured on mobile devices and email
• Not used for receiving emails. This is left to IMAP and POP3.

Question 5

What is port UDP/53 used for?

Answer 5

It is used for DNS( Domain Name System) which converts names into IP addresses - UDP/53

• E.G. www.professormesser.com = 162.159.246.164
• DNS is critical web resources for this reason DNS is usually stored on multiple DNS servers.

Question 6

What is port TCP/80 used for?

Answer 6

It is used for HTTP( Hypertext Transfer Protocol)

• tcp/80 used for Web server communication
• Your Web browser communicates to a web server when typing in addresses
• Considered “ In The Clear communication” and is not encrypted. Supported by all web servers and clients.
• Not commonly used anymore due to HTTPS being encrypted

Question 7

What is Port TCP/443 used for?

Answer 7

It is used for HTTPS( Hypertext Transfer Protocol Secure)

• tcp/443 used for Web server communication
• Your Web browser communicates to a web server when typing in addresses
• is the encrypted version which is not “ In the clear communication” like TCP port 80.
• This is the most commonly used port today for web server communication.

Question 8

What is port TCP/110 used for?

Answer 8

It is used for POP3

• This is used for receiving emails from an email server - Authenticate and transfer
• POP3( Post Office Protocol Version 3)
• tcp/110 used for basic mail transfer functionality.

Question 9

What is port TCP/143 used?

Answer 9

It is used for IMAP4( Internet Message Access Protocol v4)

• tcp/143 used for receiving emails over a an email server but provides more functionality than POP3 such as management of email inbox/ folders etc from multiple clients( e.g outlook, gmail etc)
• Can be accessed from multiple devices.

Question 10

What is port TCP/3389 used for?

Answer 10

It is used for RDP - Remote Desktop Protocol

• This shares a desktop from a remote location over port tcp/3389
• Remote Desktop Services on many Windows versions
• Can connect an entire desktop or just an application.
• Is available on Windows, MacOS, Linux, Unix, iPhone, Android and others

Question 11

What is port TCP/445 used for

Answer 11

It is used for SMB(Server Message Block direct communication. )
- Direct SMB communication over TCP without the Netbios transport

Question 12

What is port UDP/137 used for?

Answer 12

It is used for SMB older Windows Systems for NetBIOS over TCP/UDP)
- udp/137 Used to find a device on a network by its name via NetBIOS name services(nb name)

Question 13

What is port UDP/138 used for?

Answer 13

It is used for SMB on older Windows Systems for NetBIOS over TCP/UDP)
- udp/138 used for NetBIOS datagram service( nbdatagram)

Question 14

What is port TCP/139 used for?

Answer 14

It is used by SMB on older Windows Systems for NetBIOS over TCP/UDP)
- tcp/139 - used for NetBIOS session service( nbsession)

Question 15

What is port TCP/548 used for?

Answer 15

It is used for AFP( Apple Filing Protocol)

• File services for MacOS
• tcp/548
• Works with SLP( Service Location Protocol) to populate a list of available devices
• Used for file management ( e.g copy, move, delete files etc)

Question 16

What are ports TCP/427 and UDP/427 used for?

Answer 16

They are used for SLP( Service Location Protocol) which populates a list of available devices using AFP( Apple Filing Protocol) for MacOS.

Question 17

What are ports UDP/67 and UDP/68 used for?

Answer 17

They are used for DHCP( Dynamic Host Configuration Protocol)

• Automated configuration of IP Addresses, subnet mask and other options
• This requires an DHCP server
• IP addresses are assigned in real time from a pool
• Each system given a lease and must renew at set intervals
• Can also be used for DHCP reservation which reserves an IP address for a specific device via it’s MAC address

Question 18

What is port TCP/389 used for?

Answer 18

It is used for LDAP( Lightweight Directory Access Protocol)

• tcp/389 used to Store and retrieve information in a network directory used as usernames and passwords for users on the network
• Commonly used in Microsoft Active Directory.

Question 19

What is port UDP/161 used for?

Answer 19

It is used for SNMP( Simple Network Management Protocol)

• Used to gather statistics from network devices
• udp/161 is used specifically for SNMP Queries
• Can be many versions of SNMP v1 - Is the original version and provides structured tables and was in-the-clear-communication and non encrypted
• v2 was a good step ahead provided data type enhancements/ bulk transfers but Still in-the-clear communication
• v3 Is now the secure standard
• Provides message integrity
• Authentication
• Encryption

Question 20

What is port UDP/162 used for?

Answer 20

It is used for SNMP( Simple Network Management Protocol)

• Used to gather statistics from network devices
• udp/162 is used specifically for SNMP Traps or alarms
• Can be many versions of SNMP v1 - Is the original version and provides structured tables and was in-the-clear-communication and non encrypted
• v2 was a good step ahead provided data type enhancements/ bulk transfers but Still in-the-clear communication
• v3 Is now the secure standard
• Provides message integrity
• Authentication
• Encryption

Question 21

What are the secure ports used for SMTP?

Answer 21

• Port 587 is now the standard. 465 used to be used but has now been deprecated.

Question 22

What is the secure port used for POP3?

Answer 22

• Secure port TCP/995

Question 23

What is the secure port used for IMAP?

Answer 23

• Secure port TCP/993

Question 24

What is the difference between TCP and UDP ports?

Answer 24

• TCP ports are known as connection orientated(Handshake required) sessions. Each packet is checked for delivery and involves a 3 stage process of Sync, Sync and Acknowledge and finally Client acknowledgement
• UDP ports are defined as connectionless sessions, they don’t await confirmation of transmission. E.g. streaming media. There is no hand shake. .

Question 25

What port is used for more secure version of LDAP

Answer 25

• TCP port 636

Question 26

What are ports TCP/UDP 989/990 used for

Answer 26

• FTPS ( File Transfer Protocol Secure)

- Commonly used more in organizations now to ensure secure transmission of files over a network.