2.1 - Common Network Ports

Question 1

FTP – File Transfer Protocol

Answer 1

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

SSH - Secure Shell

Answer 2

• Encrypted communication link - tcp/22

* Looks and acts the same as Telnet

Question 3

Telnet

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

SMTP - Simple Mail Transfer Protocol

Answer 4

• 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 5

DNS - Domain Name System

Answer 5

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 6

HTTP and HTTPS

Answer 6

• Hypertext Transfer Protocol - tcp/80
• Communication in the browser
• And by other applications
• In the clear or encrypted - HTTPS - tcp/443
• Supported by nearly all web servers and clients

Question 7

POP / IMAP

Answer 7

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 management of email inbox
from multiple clients

Question 8

RDP - Remote Desktop Protocol

Answer 8

• 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 9

SNMP - Simple Network Management Protocol

Answer 9

• 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 10

LDAP (Lightweight Directory Access Protocol)

Answer 10

tcp/389
• Store and retrieve information in a network directory
• Commonly used in Microsoft Active Directory

Question 11

DHCP reservation

Answer 11

Addresses are assigned by MAC address
in the DHCP server
• Quickly manage addresses from one location

Question 12

• Dynamic / pooled

Answer 12

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

Question 13

DHCP - Dynamic Host Configuration Protocol

Answer 13

• 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

Question 14

AFP (Apple Filing Protocol)

Answer 14

• File services in macOS
• tcp/548
• Works with SLP (Service Location Protocol)
• tcp/427 and udp/427
• Populates the list of available devices
• File management
• Copy, move, delete files

Question 15

SMB - Server Message Block

Answer 15

• Protocol used by Microsoft Windows
• File sharing, printer sharing
• Also called CIFS (Common Internet File System)
• Using NetBIOS over TCP/IP
• udp/137 - NetBIOS name services (nbname)
• udp/138 - NetBIOS datagram service (nbdatagram)
• tcp/139 - NetBIOS session service (nbsession)
• Direct over tcp/445 (NetBIOS-less)
• Direct SMB communication over TCP
without the NetBIOS transport