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3. TCP works in the Transport layer while HTTP works in Application layer of TCP/IP model. This just means that HTTP works on top of TCP. TCP is in charge of setting up a reliable connection between two machines and HTTP uses this connection to transfer data between the server and the client. HTTP is used for transferring data while TCP is in charge of setting up a connection which should be used by HTTP in the communication process. Without TCP, HTTP cannot function (to be crisp).

4. HTTP is a top layer(application layer) protocol that takes the payload(data of user), adds it's own header bits(required for control purposes) and passes down the package to a layer below. TCP is a middle layer protocol whose main job is to chop the payload coming from above layers into multiple segments so that they can be transmitted(because there are packet size limitations, MTU-maximum transmission unit). TCP adds it's own header bits to each of the segments and then passes them to the layer below.

5. Also, Look at the steps below in a high level that occurs at the background when a user tried to access a website.

DNS Resolution -> TCP Handshake -> HTTP using the connection to exchange information between two machines.

6. TCP is a protocol that controls reliable and smooth transfer of DATA from source host :port to a destination host:port. It takes care of in-order and reliable delivery of a BYTESTREAM of data. It does NOT interpret the bytes within the DATA. TCP also employs rate control mechanisms (cong. mgmt.) in order to use the network BW optimally while at the same time be not greedy.

HTTP on the other hand is only interested in using the BYTESTREAM to demarcate it into messages between a WebServer and WebClient/browser. It uses TCP to transfer the messages, so it doesn’t have to worry about sequence, reliability or worry about the size of message. There are command primitives like GET, POST, etc., for client to communicate with server and request which data it wants from the server.

7. To use an analogy, TCP is your Postal Service, and HTTP is your letters, words, messages, requests and commands that go into the envelopes. The Postal Service just focuses on delivering the letter to the sender..

These are the five layers of the TCP/IP networking model, but they are really only conceptual. The OSI model has 7 layers. In reality, some protocols shim between various layers, or can work at multiple layers at once. TLS/SSL for instance provides encryption and session information between the network and transport layers. Above the application layer, Application Programming Interfaces (APIs) govern communication with web applications like Quora, Twitter, and Facebook.

Authors: T. C. Okenna
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Network Ports and Protocols and What They’re Used For

With more than 65,000 port numbers in existence, a list of common networking ports is not only helpful, but necessary. Especially if you’re studying for a networking certification exam like the Network+ or the CCNA. Both of these exams will test your knowledge of common ports and their associated services. 

As a component of the Transport Layer (Layer 4 in the OSI model), TCP and UDP ports are the virtual places where network connections begin and end. Port numbers allow network-connected devices to transmit data using transmission protocols. Without port numbers, network traffic would be indecipherable.

This list of common TCP and UDP ports is by no means exhaustive, but does include ports that network administrators will be expected to use in their day-to-day role.

List of Common Ports and Protocols

Port Number	Service Name	Description	Protocol
Ports 20-21	FTP	File Transfer Protocol	TCP
Port 22	SSH	Secure Shell; used for secure logins, file transfers, and port forwarding	TCP
Port 23	Telnet	Telnet protocol; used for unencrypted text communications	TCP / UDP
Port 25	SMTP	Simple Mail Transfer Protocol, used for email routing between mail servers	TCP
Port 37	Time	Used to provide a machine-readable date and time, usually for synchronizing clocks	TCP / UDP
Port 49	TACACS	Terminal Access Controller Access-Control System	TCP / UDP
Port 53	DNS	Domain Name System; translates 'host names' into IP addresses	TCP / UDP
Port 69	TFTP	Trivial File Transfer Protocol	UDP
Port 80	HTTP	Hypertext Transfer Protocol; used for unencrypted web traffic	TCP
Port 88	Kerberos	Used for secure network authentication, especially in Active Directory environments	TCP / UDP
Port 102	ISO-TSAP	ISO Transport Service Access Point (TSAP)	TCP / UDP
Port 110	POP3	Post Office Protocol; used to connect to a mail server to retrieve emails	TCP / UDP
Port 111	rpcbind	Portmapper service used to map RPC program numbers to network port numbers, typically used in NFS and other RPC services.	TCP / UDP
Port 123	NTP	Network Time Protocol	UDP
Port 135	DCE/RPC Endpoint Mapper	Distributed Computing Environment / Remote Procedure Call (DCE/RPC) Endpoint Mapper	TCP / UDP
Port 139	NetBIOS-ssn	NetBIOS Session Service	TCP / UDP
Port 161	SNMP-agents	Simple Network Management Protocol; agents communicate on this port	TCP / UDP
Ports 381 - 383	HP Performance Data Collector	Collects performance data from managed nodes	TCP / UDP
Port 389	LDAP	Lightweight Directory Access Protocol	TCP / UDP
Port 443	HTTPS	Hypertext Transfer Protocol Secure; used for encrypted web traffic	TCP / UDP
Port 445	Microsoft DS SMB	Microsoft Directory Services; TCP used for AD and Windows shares, UDP for SMB file-sharing	TCP / UDP
Port 464	Kerberos	Used for changing or setting passwords in Kerberos-based authentication systems, such as Active Directory	TCP / UDP
Port 465	SMTP	Simple Mail Transfer Protocol; used to securely transmit mail messages from email clients to email servers.	TCP
Port 514	syslog	Syslog Protocol; for collecting and organizing all log files sent from various devices on a network	UDP
Port 587	SMTP	Simple Mail Transfer Protocol; used for email message submission	UDP
Port 593	RPC Mapper Service	Enables secure remote connections and function execution over HTTP.	TCP / UDP
Port 636	LDAP / LDAPS	Lightweight Directory Access Protocol (over SSL); used to store data in the LDAP directory and authenticate users to access the directory	TCP / UDP
Port 691	Microsoft Exchange Routing Engine (RESvc)	Used by Microsoft Exchange servers to update routing tables for efficient message delivery.	TCP
Port 902	VMware vSphere	Used to manage your ESXi hosts and the virtual machines (VMs) that run on them	TCP / UDP
Port 993	IMAP	Internet Message Access Protocol; used to deliver and manage messages on email servers on behalf of email clients	TCP
Port 995	POP3	Post Office Protocol version 3 (over SSL); lets email users download messages from an email server using an email client	TCP / UDP
Port 1194	OpenVPN	Used by OpenVPN for establishing encrypted tunnels between VPN clients and servers	TCP / UDP
Port 1433	Microsoft SQL Server	Allows encrypted access to and management of databases and servers	TCP
Port 1521	Oracle Database	Oracle client apps communicate with Oracle database servers	TCP
Port 3306	MySQL	Used to connect with MySQL clients and utilities	TCP
Port 3389	Remote Desktop Protocol	Allows client device to remotely access and control a Windows desktop computer over this port	TCP
Port 5060	SIP	Session Initiation Protocol; used to signal and control communication sessions	TCP / UDP
Port 5353	mDNS	Multicast DNS (mDNS) is used for resolving hostnames to IP addresses within small networks without a local DNS server.	UDP
Port 5432	PostgreSQL	Used for communication between PostgreSQL clients and the database server	TCP
Port 5900	VNC (Virtual Network Computing)	Used for remote desktop sharing, allows a client to remotely view and control another computer's desktop	TCP
Ports 6665-6669	IRC (Internet Relay Chat)	Used for Internet Relay Chat (IRC) communications, enabling text-based communication over networks	TCP / UDP
Ports 6881-6999	BitTorrent	Used for peer-to-peer file sharing, facilitating data distribution across networks	TCP / UDP
Ports 8086 & 8087	TTP Alternate/IoT Services	These ports are often used as alternative ports for web servers, IoT (Internet of Things) services, or internal applications.	TCP
Port 9100	Printer/JetDirect	Commonly used by network printers and print servers for raw printing protocols	TCP
Port 10000	Webmin	Used for remote server communication and configuration	TCP
Port 12345	NetBus	Used for remote administration; can be exploited for unauthorized access	TCP / UDP
Port 31337	Back Orifice / ncat	Used for remote control of servers by hacking tools and remote administration utilities	TCP / UDP

Understanding TCP and UDP Protocols: Frequently Asked Questions

Ports and their affiliated numbers are used to identify specific applications and services. Port numbers are what allow apps on an IP network to communicate with the source and destination IP address and the transport protocol.

What is a Port Number?

Networking protocols use port numbers that are based on the type of packet being sent and/or received. A network host typically runs many software packages/processes, so when it receives a packet it looks to the port number to identify which process should get it.

How Do Port Numbers Work?

All network-connected devices are affiliated with a port that’s been assigned a number. These port numbers are standardized, and each is reserved for certain protocols. 

Port identification numbers are used to ensure the correct information is being sent and received. For example, one port is used to send the packet, while another port is used to receive the data.

All port numbers target a service or application and are reserved for certain protocols.

Where Do Ports Fall Into the OSI Model?

Ports are a concept of Layer 4 — the Transport Layer. Transport protocols such as TCP and UDP indicate the port that a packet should go to. 

What Are Well-Known/Systems Ports?

Port numbers that fall into the category of well-known/system ports include numbers between 0 and 1023. IP protocols use them for TCP, UDP, Telnet, and FTP. 

These port numbers are only used by network admins, default applications, operating systems, and services. Users do not have access to this range of ports.

What are Registered Port Numbers?

The next range of port numbers after well-known ports includes ports 1024 through 49151. This range of ports is known as “Registered ports” because they are registered with the IANA (Internet Assigned Numbers Authority).

Unlike well-known port numbers, registered port numbers are used by network users. 

What Are Dynamic/Private Port Numbers?

The final range of port numbers falls between 49152 and 65535. Unlike well-known or registered port numbers, these ports can be used without any restriction.

Authors: T. C. Okenna
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TCP/IP Ports and Protocols

One of the many fundamental things to know as a network engineer is the function and port number used by a number of common services as well as many that are typically implemented during the course of a network engineer’s career. Below, we take a look at these protocols, provides a basic description of their function, and lists the port numbers that they are commonly associated with.

Table 1
Common TCP/IP Protocols and Ports

Protocol	TCP/UDP	Port Number	Description
File Transfer Protocol (FTP) (RFC 959)	TCP	20/21	FTP is one of the most commonly used file transfer protocols on the Internet and within private networks. An FTP server can easily be set up with little networking knowledge and provides the ability to easily relocate files from one system to another. FTP control is handled on TCP port 21 and its data transfer can use TCP port 20 as well as dynamic ports depending on the specific configuration.
Secure Shell (SSH) (RFC 4250-4256)	TCP	22	SSH is the primary method used to manage network devices securely at the command level. It is typically used as a secure alternative to Telnet which does not support secure connections.
Telnet (RFC 854)	TCP	23	Telnet is the primary method used to manage network devices at the command level. Unlike SSH which provides a secure connection, Telnet does not, it simply provides a basic unsecured connection. Many lower level network devices support Telnet and not SSH as it required some additional processing. Caution should be used when connecting to a device using Telnet over a public network as the login credentials will be transmitted in the clear.
Simple Mail Transfer Protocol (SMTP) (RFC 5321)	TCP	25	SMTP is used for two primary functions, it is used to transfer mail (email) from source to destination between mail servers and it is used by end users to send email to a mail system.
Domain Name System (DNS) (RFC 1034-1035)	TCP/UDP	53	The DNS is used widely on the public internet and on private networks to translate domain names into IP addresses, typically for network routing. DNS is hieratical with main root servers that contain databases that list the managers of high level Top Level Domains (TLD) (such as .com). These different TLD managers then contain information for the second level domains that are typically used by individual users (for example, cisco.com). A DNS server can also be set up within a private network to private naming services between the hosts of the internal network without being part of the global system.
Dynamic Host Configuration Protocol (DHCP) (RFC 2131)	UDP	67/68	DHCP is used on networks that do not use static IP address assignment (almost all of them). A DHCP server can be set up by an administrator or engineer with a poll of addresses that are available for assignment. When a client device is turned on it can request an IP address from the local DHCP server, if there is an available address in the pool it can be assigned to the device. This assignment is not permanent and expires at a configurable interval; if an address renewal is not requested and the lease expires the address will be put back into the poll for assignment.
Trivial File Transfer Protocol (TFTP) (RFC 1350)	UDP	69	TFTP offers a method of file transfer without the session establishment requirements that FTP uses. Because TFTP uses UDP instead of TCP it has no way of ensuring the file has been properly transferred, the end device must be able to check the file to ensure proper transfer. TFTP is typically used by devices to upgrade software and firmware; this includes Cisco and other network vendors’ equipment.
Hypertext Transfer Protocol (HTTP) (RFC 2616)	TCP	80	HTTP is one of the most commonly used protocols on most networks. HTTP is the main protocol that is used by web browsers and is thus used by any client that uses files located on these servers.
Post Office Protocol (POP) version 3 (RFC 1939)	TCP	110	POP version 3 is one of the two main protocols used to retrieve mail from a server. POP was designed to be very simple by allowing a client to retrieve the complete contents of a server mailbox and then deleting the contents from the server.
Network Time Protocol (NTP) (RFC 5905)	UDP	123	One of the most overlooked protocols is NTP. NTP is used to synchronize the devices on the Internet. Even most modern operating systems support NTP as a basis for keeping an accurate clock. The use of NTP is vital on networking systems as it provides an ability to easily interrelate troubles from one device to another as the clocks are precisely accurate.
NetBIOS (RFC 1001-1002)	TCP/UDP	137/138/139	NetBIOS itself is not a protocol but is typically used in combination with IP with the NetBIOS over TCP/IP (NBT) protocol. NBT has long been the central protocol used to interconnect Microsoft Windows machines.
Internet Message Access Protocol (IMAP) (RFC 3501)	TCP	143	IMAP version3 is the second of the main protocols used to retrieve mail from a server. While POP has wider support, IMAP supports a wider array of remote mailbox operations which can be helpful to users.
Simple Network Management Protocol (SNMP) (RFC 1901-1908, 3411-3418)	TCP/UDP	161/162	SNMP is used by network administrators as a method of network management. SNMP has a number of different abilities including the ability to monitor, configure and control network devices. SNMP traps can also be configured on network devices to notify a central server when specific actions are occurring. Typically, these are configured to be used when an alerting condition is happening. In this situation, the device will send a trap to network management stating that an event has occurred and that the device should be looked at further for a source to the event.
Border Gateway Protocol (BGP) (RFC 4271)	TCP	179	BGP version 4 is widely used on the public internet and by Internet Service Providers (ISP) to maintain very large routing tables and traffic processing. BGP is one of the few protocols that have been designed to deal with the astronomically large routing tables that must exist on the public Internet.
Lightweight Directory Access Protocol (LDAP) (RFC 4510)	TCP/UDP	389	LDAP provides a mechanism of accessing and maintaining distributed directory information. LDAP is based on the ITU-T X.500 standard but has been simplified and altered to work over TCP/IP networks.
Hypertext Transfer Protocol over SSL/TLS (HTTPS) (RFC 2818)	TCP	443	HTTPS is used in conjunction with HTTP to provide the same services but doing it using a secure connection which is provided by either SSL or TLS.
Lightweight Directory Access Protocol over TLS/SSL (LDAPS) (RFC 4513)	TCP/UDP	636	Just like HTTPS, LDAPS provides the same function as LDAP but over a secure connection which is provided by either SSL or TLS.
FTP over TLS/SSL (RFC 4217)	TCP	989/990	Again, just like the previous two entries, FTP over TLS/SSL uses the FTP protocol which is then secured using either SSL or TLS.

Summary

While it may seem obvious that there are large number of ports that are missing from this list, the purpose here was to just cover the most commonly seen and used protocols. The complete list of assigned ports and their assigned services can be seen at http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xml. Hopefully the contents of this article will help in determining the correct port number to use when implementing these services.

Authors: T. C. Okenna
Register for this course: Enrol Now

Authors: T. C. Okenna
Register for this course: Enrol Now

What are Network Port Numbers?

Port numbers are integral components of the Internet's communication protocol. They act like virtual endpoints for network connections, enabling multiple applications on a single device to share the same network interface.

Port numbers serve as identifiers for protocols and applications, enabling efficient data routing, service identification, and security management in computer networks. The combination of IP addresses and port numbers allows for end-to-end communication between applications across devices.

This article covers the concept of port numbers, their types, and their importance in computer networking. It also provides a list of 25 common network port numbers that you should know.

What is a Port Number?

A computer port number is a 16-bit integer that serves as a unique identifier for a specific process or service on a networked device. It allows multiple applications to communicate simultaneously over the same IP address by directing incoming data to the appropriate application.

Port numbers range from 0 to 65535. While port 0 is reserved and not used for direct communication, the remaining ports are utilized for various protocols and services in networking.

Types of Port Numbers

There are 3 types of port numbers based on the port number ranges:

1. Well-Known Ports (0-1023): Reserved for widely used services and protocols. Examples include:

● HTTP (Port 80)

● HTTPS (Port 443)

● FTP (Port 21)

2. Registered Ports (1024-49151): Assigned to specific applications by organizations. These ports are not as universally recognized but are commonly used.

3. Dynamic/Private Ports (49152-65535): Typically used for temporary connections and can be utilized by any process.

Network Ports Functioning with TCP/UDP

In TCP and UDP communication, port numbers are essential for directing data packets to the correct applications on devices. Each port number, ranging from 0 to 65535, identifies specific services and applications.

TCP Communication Process:

1. Connection Establishment: When a client wants to communicate with a server, it uses a combination of the server's IP address and the designated port number (e.g., port 80 for HTTP). The client selects a random unused port number for its end of the connection.

2. Data Transmission: Once the connection is established, data packets are sent back and forth between the client and server using their respective port numbers, ensuring reliable delivery through acknowledgments and retransmissions.

UDP Communication Process:

1. Connectionless Communication: Unlike TCP, UDP does not establish a connection before sending data. The client sends packets to the server's IP address and port number directly.

2. Data Transmission: Each packet includes the source and destination port numbers, allowing the server to differentiate between various types of data (e.g., video streams or control messages) without ensuring delivery reliability.

List of Common Port Numbers

Here is a table listing 25 common port numbers with their associated services, usage, and protocols:

Port Number	Service	Used For	Protocol
20	FTP-DATA	File Transfer	TCP
21	FTP	File Transfer Control	TCP
22	SSH	Secure Remote Login	TCP
23	Telnet	Unencrypted Remote Access	TCP
25	SMTP	Email Routing	TCP
53	DNS	Domain Name Resolution	UDP/TCP
67	DHCP-S	DHCP Server	UDP
68	DHCP-C	DHCP Client	UDP
69	TFTP	Trivial File Transfer	UDP
80	HTTP	Web Traffic	TCP
110	POP3	Email Retrieval	TCP
123	NTP	Time Synchronization	UDP
143	IMAP	Email Management	TCP
443	HTTPS	Secure Web Traffic	TCP
3306	MySQL	Database Service	TCP
3389	RDP	Remote Desktop Access	TCP
5432	PostgreSQL	Database Service	TCP
5060	SIP	VoIP Communication	UDP/TCP
5900	VNC	Remote Desktop Sharing	TCP
8080	HTTP-ALT	Alternative Web Traffic	TCP
2049	NFS	Network File System	TCP/UDP
161	SNMP	Network Management	UDP
162	SNMP-TRAP	SNMP Trap Messages	UDP
445	SMB	File Sharing	TCP
27017	MongoDB	Database Service	TCP
5000	UPnP	Universal Plug and Play	UDP/TCP

Importance of Port Numbers in Networking

As we discussed above, the role of Port numbers is very crucial in networking. It facilitates effective communication and data exchange between different devices and applications within a network.

Here are the 6 reasons why port numbers are needed:

1. Multiplexing and Demultiplexing:

In a single device, multiple applications may be sending and receiving data over the network simultaneously. Port numbers allow the operating system to route incoming data to the correct application through a process called demultiplexing.

Conversely, when sending data, port numbers allow multiplexing, ensuring that data from various applications is transmitted through the appropriate ports. This mechanism is crucial for efficient communication in networking, as it helps distinguish between different services and applications using the same network interface.

2. End-to-End Communication:

As the name suggests, Port numbers help establish end-to-end communication between devices across a network. When a device initiates a connection, it specifies both its IP address and a source port number, and the destination device responds with its IP address and a destination port number.

This combination allows data to be routed accurately to the intended application on the receiving device.

3. Protocol Identification:

Port numbers are used to identify the specific protocol or service that an application is using. Well-known port numbers are associated with common services such as HTTP (port 80), HTTPS (port 443), FTP (port 21), and more.

By using these standard port numbers, devices can quickly recognize the type of communication being established and handle data accordingly.

4. Security and Firewalls:

When we talk about security, Port numbers are very important for implementing network security measures such as firewalls. Firewalls can filter and control network traffic based on port numbers.

For example, a firewall might be configured to allow web traffic (HTTP) on port 80 while blocking other ports to prevent unauthorized access or potential threats.

5. Load Balancing:

In scenarios where multiple servers are serving the same application, load balancing distributes incoming network traffic across these servers to optimize performance and prevent overload. Port numbers are often used to route traffic to different servers based on load-balancing algorithms.

6. Custom Application Communication:

Developers can use custom port numbers to establish communication channels for their specific applications or services. This enables the creation of unique network services tailored to specific needs.

Computer Port Numbers - Summing Up!!

Computer port numbers are vital for network communication, allowing multiple applications to run simultaneously on a device. Ranging from 0 to 65535, they are categorized into well-known ports (0-1023), registered ports (1024-49151), and dynamic/private ports (49152-65535).

Well-known ports are reserved for standard services like HTTP (port 80) and FTP (port 21). Understanding port numbers is essential for effective data routing, multiplexing, and demultiplexing, ensuring that incoming data reaches the correct application or service on a device efficiently.

Authors: Jitendra, T. C. Okenna
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