CompTIA A+ 220-1201 (2.1 - Common Ports)

Port numbers

• Well-known port number

- Client and server need to match

• Important for firewall rules

- Port-based security

• A bit of rote memorization

- Becomes second nature after a while

• Make sure you know port number, protocol,

and how the protocol is used

FTP - 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.

SSH - Secure Shell

• Encrypted communication link - tcp/22

• Looks and acts the same as Telnet

Telnet

• Telnet - Telecommunication Network - tcp/23

• Login to devices remotely

- Console access

• In-the-clear communication

- Not the best choice for production systems

SMTP - Simple Mail Transfer Protocol

• 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

DNS - 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

DHCP - 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

HTTP and HTTPS

• Hypertext Transfer Protocol

- Communication in the browser

- And by other applications

• In the clear or encrypted

- Supported by nearly all web servers and clients

POP3 / IMAP

• 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

SMB - Server Message Block

• Protocol used by Microsoft Windows

- File sharing, printer sharing

- Also called CIFS (Common Internet File System)

• Using NetBIOS over TCP/IP

(Network Basic Input/Output System)

- udp/137 - NetBIOS name services (nbname)

- tcp/139 - NetBIOS session service (nbsession)

• Direct over tcp/445 (NetBIOS-less)

- Direct SMB communication over TCP without

the NetBIOS transport

LDAP/LADPS

• LDAP (Lightweight Directory Access Protocol)

- tcp/389

- Store and retrieve information in a network directory

- Commonly used in Microsoft Active Director

RDP - 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

Common Ports - Chart