In this article, I will discuss various protocols and port numbers and the usage of protocols. Some of the most common protocols are summarized below
Que. – What is a port?
- If you look at the back of your computer, you’ll see USB ports, HDMI ports, VGA ports, and probably a single network (Ethernet) port. We’re not talking about those ports.
- A port is simply a virtual channel that an application can use to communicate with a specific protocol. All the data entering your computer travels through that single physical Ethernet port (or through a Wi-Fi connection), but it must be separated somehow so that every application receives the information it needs.
- Port Numbers/Name and Usage port is reserved for only one protocol, and the applications that use a protocol will use the ports reserved for that protocol.
- There are 65,535 different ports.
1. 20 and 21/FTP (File Transfer Protocol)
- FTP is a protocol for transferring files between two devices
- FTPS adds a security layer to the file transfer. It requires that the server have an SSL certificate installed. The entire session can be encrypted or only specific portions of the session can be encrypted.
2. 22/SSH (Secure Shell)
- Secure Socket Shell (or Secure Shell) allows a user to connect to a remote computer. SSH authenticates the identity of the remote computer to the user and the user to the remote computer.
- SSH creates a tunnel between the user and the remote computer. The user will require an SSH client such as PuTTY, and the remote computer will require an SSH daemon.
- Each remote computer must be set up to accept SSH logins (typically over port 22). Network firewalls must be configured to allow traffic over port 22. The user’s IP address should be whitelisted on the firewall (do not allow SSH connections from any IP address)
3. 22/SFTP (SSH File Transfer)
- SFTP is a file transfer protocol within the SSH protocol. Provided that the SSH session is secured and properly configured, then the SFTP session will be as well.
4. 23/Telnet (Telnet)
- Telnet provides a text-based terminal to communicate with a network device or server. Telnet is like SSH but does not contain any security.
- It is no longer popular due to a lack of security.
5. 25/SMTP (Simple Mail Transfer Protocol)
- Used to communicate with an e-mail server (for sending e-mail only).
- Can be secure or insecure, depending on whether the client and server agree to encrypt data between them.
6. 53/DNS (Domain Name Server)
- Translates Domain Names/Hostnames to IP addresses (necessary to locate network resource)
- Consider that a human can remember text names (such as google.ca or amazon.com), but for a web browser to access a website, it must figure out the corresponding server IP address.
- The DNS converts human-readable domain names into machine-readable IP addresses.
7. 67/68/DHCP (Dynamic Host Configuration Protocol)
- Allows a device to request a dynamic IP from a DHCP server. It Allows a DHCP server to dynamically assign IP addresses to other devices.
- When a device first joins a network, it may not need an IP address and must request one.
8. 69/TFTP (Trivial File Transfer Protocol )
- TFTP is like FTP in that it allows a user to transfer files over a network. TFTP has a simple design.
- An important use of TFTP is to allow a device to boot over a network. A device with no operating system can load one over the network into memory.
9. 80/HTTP (HyperText Transfer Protocol)
- Used to transmit web site data (insecure)
10. 110/POP (Post Office Protocol)
- It allows an e-mail client like Outlook to retrieve messages from a server. With POP, the e-mail server receives messages on behalf of the user. The e-mail client asks the server if there are any new messages. If so, the e-mail client downloads messages from the server. The server deletes the messages after they have been downloaded.
- POP is no longer common; it has been replaced with IMAP and Exchange, which allow an e-mail client to “sync” with a server.
11. 123/NTP (Network Time Protocol)
- NTP allows network-connected devices to sync their clocks, to within a few milliseconds of UTC. NTP can function accurately even when the network has high latency through the clock synchronization algorithm.
- NTP can obtain the time from a central server or from a peer.
12. 143/IMAP (Internet Message Access Protocol)
- It allows an e-mail client to communicate with an e-mail server. The client and server “sync” so that both have the same data (e-mails, calendar entries, contacts, etc.).
- If an e-mail is deleted in the e-mail client, then it is also deleted on the server.
- IMAP may be secure or insecure.
13. 161/162/SNMP (Simple Network Management Protocol)
- Allows a user to collect and manage data about manage network devices, including routers, switches, servers, and printers.
14. 389/LDAP (Lightweight Directory Access Protocol)
- Allows users to access different directories
- Directories include e-mail directories, users, phone numbers, printers, and services
15. 427/SLP (Service Location Protocol)
- Allows computers to find services on a local network
- A device will broadcast a URL containing the location of a service that it offers over SLP
Other devices can connect to the URL over SLP to use the service
16. 443/HTTPS (HyperText Transfer Protocol-Secure)
- Used to transmit web site data (secure)
17. 445/SMB/CIFS (Server Message Block/Common Internet File System)
- Allows computers on a network to share files and printers
18. 548/AFP (Apple Filing Protocol)
- Allows Apple devices to share files
19. 636/LDAPS (Secure Lightweight Directory Access Protocol)
- Like LDAP but secure
20. 3389/RDP (Remote Desktop Protocol)
- Allows a user to remotely connect to a Windows server or computer via a Graphical User Interface
21. 5060/5061/SIP (Session Initiation Protocols)
- Used for real-time communications involving VoIP and video conferencing. Also used by mobile devices for voice over LTE
22. ICMP (Internet Control Message Protocol)
- ICMP is a special protocol. It does not carry user traffic, but machine-to-machine communications.
- Network equipment uses ICMP messages to communicate errors and status updates with each other.
- ICMP messages are used by ping and tracert commands.
- These commands are important for network troubleshooting.
- It was designed to communicate network-layer information between hosts and routers, not between application-layer processes. so it doesn’t have port no.
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