Common Network Ports

Question 1

What is the FTP port? (name, number and function)

Answer 1

File Transfer Protocol

tcp/20 (active mode data), tcp/21 (control)

– Transfers files between systems
* Authenticates with a username and password
– Some systems use a generic/anonymous login
* Full-featured functionality - List, add, delete, etc.

Question 2

What is the SSH port? (name, number and function)

Answer 2

Secure Shell
Encrypted communication link - tcp/22
* Looks and acts the same as Telnet

Question 3

What is the Telnet port? (name, number and function)

Answer 3

Telnet – Telecommunication Network - tcp/23
* Login to devices remotely
– Console access
* In-the-clear communication
– Not the best choice for production systems

Question 4

What is the SNMP port? (name, number and function)

Answer 4

Simple Network Management Protocol

Gather statistics from network devices
– Queries: udp/161
– Traps: udp/162

• v1 – The original
  – Structured tables
  – In-the-clear
• v2 – A good step ahead
  – Data type enhancements
  – Bulk transfers
  – Still in-the-clear
• v3 – A secure standard
  – Message integrity
  – Authentication
  – Encryption

Question 5

What is the SMTP port? (name, number and function)

Answer 5

• SMTP - Simple Mail Transfer Protocol
  – Server to server email transfer - tcp/25
• Also used to send mail from a device to a mail server
  – Commonly configured on mobile devices and email clients
• Other protocols are used for clients to receive email
  – IMAP, POP3

Question 6

What is the DNS port? (name, number and function)

Answer 6

Domain Name System

• Converts names to IP addresses - udp/53

– www.professormesser.com = 162.159.246.164
* These are very critical resources
– Usually multiple DNS servers are in production

Question 7

What is the DHCP port? (name, number and function)

Answer 7

Dynamic Host Configuration Protocol

Automated configuration of IP address, subnet mask and other options
- udp/67, udp/68

– Requires a DHCP server
– Server, appliance, integrated into a SOHO router, etc.

• Dynamic / pooled
  – IP addresses are assigned in real-time from a pool
  – Each system is given a lease and must renew at set intervals
• DHCP reservation
  – Addresses are assigned by MAC address in the DHCP server
  – Manage addresses from one location

Question 8

What is the HTTP and HTTPS port? (name, number and function)

Answer 8

Hypertext Transfer Protocol
tcp/80

Hypertext Transfer Protocol Secure
tcp/443

– Communication in the browser
– And by other applications
* In the clear or encrypted
– Supported by nearly all web servers and clients

Question 9

What is the POP3 / IMAP port? (name, number and function)

Answer 9

• Receive emails from an email server
  – Authenticate and transfer
• POP3 - Post office Protocol version 3
  – tcp/110
  – Basic mail transfer functionality
• IMAP4 - Internet Message Access Protocol v4
  – tcp/143
  – Includes email inbox management from multiple clients

Question 10

What is the SMB port? (name, number and function)

Answer 10

Server Message Block
tcp/445

Protocol used by Microsoft Windows
– File sharing, printer sharing
– Also called CIFS (Common Internet File System)

Question 11

What is the LDAP port? (name, number and function)

Answer 11

LDAP (Lightweight Directory Access Protocol) - tcp/389

• Store and retrieve information in a network directory
  – Commonly used in Microsoft Active Directory

Question 12

What is the RDP port? (name, number and function)

Answer 12

Remote Desktop Protocol

• Share a desktop from a remote location over tcp/3389
• Remote Desktop Services on many Windows versions
• Can connect to an entire desktop or just an application
• Clients for Windows, macOS, Linux, Unix, iPhone,
  Android, and others

Question 13

What is the NetBIOS over TCP/IP port? (name, number and function)

Answer 13

(Network Basic Input/Output System)
– udp/137 - NetBIOS name services (nbname)
– tcp/139 - NetBIOS session service (nbsession