Port Numbers A+

20/21

FTP (File Transfer Protocol) The first is for data, the second is for control. TCP. Used for transferring computer files between a client and a server on a computer network. It's a common method for uploading, downloading, and managing files remotely, but is generally considered less secure and less feature-rich than modern alternatives

22

SSH (Secure Shell) a cryptographic network protocol that provides secure remote login and file transfer. It's used to establish encrypted connections between computers, protecting data transmitted over unsecured networks.

23

Telnet TCP enables users to remotely access and control another computer over a TCP/IP network. It provides a text-based command-line interface, allowing users to manage files, run programs, and interact with the remote system as if they were physically present.

25

SMTP (Simple Mail Transfer Protocol) (Unsecure) is an internet standard for sending and receiving emails. It's the protocol that allows mail servers to communicate and transfer messages between each other, enabling email communication. SMTP is used to send emails from an email client to an email server, and the server then relays the email to the recipient's server.

53

DNS (Domain Name System) acts as the Internet's address book, translating human-readable domain names (like google.com) into the numerical IP addresses that computers use to communicate.

67/68

DHCP (Dynamic Host Configuration Protocol) is a network protocol that automatically assigns IP addresses and other network configuration settings to devices on a network. It simplifies network management by dynamically allocating IP addresses as devices connect and disconnecting, making it ideal for larger networks with many devices.

80

HTTP (Hypertext Transfer Protocol) used for transferring data over the internet, particularly between web browsers and servers.

110

POP3 used for receiving email, where an email client downloads emails from a server to a local device, and then typically deletes the messages from the server. It's a one-way process, meaning the server doesn't maintain a copy of the emails after they're downloaded.

137-139

NetBIOS (Network Basic Input/Output System) enable communication and resource sharing within a local area network (LAN). Specifically, these ports handle name resolution, datagram services, and session services, allowing applications on different computers to communicate and share files and printers.

NetBIOS over TCP/IP (NetBT):

This protocol is an implementation of NetBIOS that uses TCP/IP for communication. It's used by applications to communicate on a local network, often for file and printer sharing.

Ports 137, 138, and 139:

These ports are associated with NetBIOS services:Port 137 (UDP): Used for name services, which allows computers to resolve NetBIOS names to IP addresses and vice versa. Port 138 (UDP): Used for datagram services, which provide connectionless communication between devices on the network. Port 139 (TCP): Used for session services, which establish and maintain communication sessions between computers for file and printer sharing.

143

IMAP (Internet Message Access Protocol) a protocol that allows you to access and manage email messages stored on a remote mail server. Unlike POP3, which downloads emails to your local device and removes them from the server, IMAP keeps emails on the server, allowing you to access them from multiple devices. This means changes you make on one device, like deleting or moving an email, will be reflected on all other devices.

161/162

SNMP (Simple Network Management Protocol) used for managing and monitoring network devices. It allows network administrators to collect and report data from devices like routers, switches, servers, and more, even if they have different hardware or software. SNMP operates on the application layer (OSI layer 7) and uses UDP on port 161 for requests and port 162 for notifications.

443

HTTPS (Hypertext Transfer Protocol Secure) is a secure version of the standard HTTP protocol used for transferring data over the internet. It encrypts the communication between a user's web browser and a website, ensuring data confidentiality and preventing eavesdropping or man-in-the-middle attacks.

445

SMB (Server Message Block) / CIFS (Common Internet File System) used for sharing files and printers between devices on a network. It's a client-server protocol, meaning a client requests access to resources on a server, and the server responds. SMB is a fundamental part of how data is moved and shared in networked environments, especially in data centers and virtualized servers.

3389

RDP (Remote Desktop Protocol) enables users to control and operate computers from a distance remotely. By establishing an encrypted communication channel, RDP facilitates the secure exchange of information between connected machines.

389

LDAP (Lightweight Directory Access Protocol) used for managing and accessing directory services, which are databases that store information about users, computers, and other network resources. It simplifies user management, authentication, and access control in networks.

993

secure email communication. This means your email client will use SSL/TLS encryption when connecting to the IMAP server on port 993, ensuring that your email data is protected during transmission. This is a common practice and is often used with popular email providers like Gmail, Outlook.com, and iCloud.

995

POP3S

587

SMTP (Secure)

548

AFP (Apple Filing Protocol) is Apple's proprietary file services protocol primarily used on macOS systems. Operating over TCP port 548, it facilitates secure and efficient sharing, browsing, and file management within a Macintosh network environment.

427

This includes printers, RDP, telephony services, NAS devices, and more. Let's review how the discovery process works. A conceptual understanding may help with troubleshooting down the road. Here is a scenario where a user needs SLP to print something.