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Network Layer – Functions and Protocols

Network Layer – Functions and Protocols

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The main function of the network layer is to deliver packets from source to destination across multiple networks. It also specifies the packet structure and processing used to carry the data from one host to another. The layer routes the packet through different channels to the other end and acts as a network controller.

The Network Layer also controls the operation of the subnet. If two computers are connected using the same link, then there is no need for this layer. It also provides addressing, encapsulation and de-encapsulation services to permit end devices to exchange data across the network. The network layer’s main functions, services, and protocols are as follows:

Addressing end devices

A source or destination device in a networked system. For example, Computers, laptops, file servers, web servers, Network printers, VoIP phones, Security cameras, and Mobile handheld devices. The end device address configuration is important. Without a unique IP address, there is no concept of data transmission across the network. Addressing the End device is necessary for the identification of the devices on the network.

Encapsulation

Another important network layer service is encapsulating the protocol data unit (PDU) from the transport layer into an IP packet. The encapsulation method adds IP header information, such as the IP address of the source and destination hosts. The header is used to carry the packet to the appropriate host. The IP header remains in the packet until it arrives at the destination host. The figure below illustrates how the transport layer protocol data unit (PDU) is encapsulated by the network layer protocol data unit (PDU) to create an IP packet.

Network Layer Encapsulation

The process of encapsulating data, layer by layer, enables the services at the different layers to grow and scale without disturbing the other layers. This means IPv4 or IPv6 easily packages the transport layer segments. Routers can apply these different network layer protocols to operate simultaneously over a network. The routing depends on only the contents of the network layer packet header. In all cases, the data portion of the packet; that is, the encapsulated transport layer protocol data unit (PDU) remains unchanged during the network layer processes.

De-encapsulation

When the packet is received at the network layer (Layer 3) of the destination host, the host checks the IP header of the packet. If the destination IP address and the IP address of the header match. Then, the IP header is removed from the packet. Removing of IP Header process called De-encapsulation. After the packet is de-encapsulated by the network layer, the resulting Layer 4 protocol data unit (PDU) passes upwards to Layer 4 or the transport layer.

Routing

The network layer routes packets to a destination host on another network. Router made it possible for the packet of one network to travel to another network. The router’s job is to direct the packet to its best path toward the destination host. A packet may cross many intermediary devices before reaching the destination host. Each router crosses a packet to reach the destination host, which is a hop.

Network Layer Protocols

There are several network layer protocols, which are listed below. However, here we will discuss the first two protocols in the coming article, which are commonly known as the IP address of the device or computer:

  • IPv4, also Internet Protocol version 4
  • IPv6, also known as Internet Protocol version 6
  • DDP, Datagram Delivery Protocol
  • DVMRP, Distance Vector Multicast Routing Protocol
  • ICMP, Internet Control Message Protocol
  • IGMP, Internet Group Management Protocol
  • IPsec, Internet Protocol Security
  • IPX, Internetwork Packet Exchange
  • PIM-DM, Protocol Independent Multicast Dense Mode
  • PIM-SM, Protocol Independent Multicast-Sparse Mode
  • RIP, also Routing Information Protocol
  • RSMLT Routed-SMLT
Unveiling the World of Network Protocols: A Comprehensive Guide

Unveiling the World of Network Protocols: A Comprehensive Guide

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When two humans talk to each other, they may have to use the same language but they generally understand each other without having to adhere to rigid rules of grammar or formal language frameworks. Computers, on the other hand, have everything openly defined and structured. If computers wish to communicate with another one, they have to know in advance exactly how information is to be exchanged and precisely what the format will be.

Therefore, standard methods of transmitting and processing various kinds of information are used and these methods are called “Network Protocol“. Protocols are established by international agreement and ensure that computers everywhere can talk to one another. There are many network protocols for different kinds of information and functions.

The network protocol is similar to programming languages, based on specific rules and regulations for computing and efficiency. Each rule is defined in different terms and assigned a unique protocol name. Network Protocol identifies the standards for communication and provides detailed information on processes involved in data transmission. Such processes include:

  • Type of the task
  • Nature
  • Rate of Data flow
  • Type of Data flowing
  • Device management

A single data-sending process can be handled using more than one network protocol. This coordination of network protocols creates a network protocol family. The important and well-known network protocols are :

Telnet (TN)

Telnet (TN) is an important network protocol used to access remote host resources over the Internet or a TCP/IP computer network. It stands for Teletype Network and is used to establish a remote connection using the telnet protocol. Telnet was established in 1969 and standardized as one of the first Internet standards by the Internet Engineering Task Force (IETF) for remote connection.

A host (Telnet server), runs a telnet server application (or daemon in Unix terms) that receives a connection from a remote host called the telnet client. The connection is presented to the operating system of the telnet server as though it is a terminal connection connected directly. Telnet provides text-based software providing access to the command line interface of the host computer.

Note:- Do not confuse the telnet application with the Telnet protocol. Telnet is an application layer protocol.

HTTP

HTTP stands for HyperText Transfer Protocol. It is an application layer protocol and the foundation of the World Wide Web. HTTP is used for transferring files like graphic images, sound, video, text, and other multimedia files on the web. It also defines how messages are formatted and transmitted; and what actions Web servers and browsers should take in response to different commands.

HTTP transfers Web pages and such resources from the Web Server to the Web Client using different types of a web browser such as Internet Explorer, Google Chrome, or Firefox. For example, when someone enters a URL in their web browser, this sends an HTTP command to the Web server directing it to get and transmit the requested Web page.

HTTPS

Hypertext Transfer Protocol Secure is the advanced and secure version of the Hypertext Transfer Protocol (HTTP). It is used for the secure transfer of data over a computer network and is widely used on the Internet. The “S” in HTTPS stands for “Secure”. It looks as illustrated in the image below, like the lock icon in the address bar of the web browser.

 

File Transfer Protocol (FTP)

FTP is a standard protocol for transferring files between computers on the Internet over TCP/IP connections. It provides a method for copying files over a network from one computer to another computer. It is a client-server protocol that relies on two communication channels between client and server generally.

Clients start conversations with servers requesting to download a file. Using FTP, a client can upload, download, delete, rename, move, and copy files on a server. A user classically needs to log on to the FTP server, although some servers make some or all of their content available without login, also known as anonymous FTP.

FTP provides some simple file management on the contents of a remote computer. It is an old protocol; used less than it was before the World Wide Web came along. Nowadays, its main usage is to upload files to a Web site. Sites that have a lot of downloading like software sites often have an FTP server to handle the traffic. If FTP is involved, the URL will have FTP at the front.

TFTP

TFTP stands for Trivial File Transfer Protocol and it is the simplest version of FTP. Where FTP allows a user to see a directory listing perform some directory-related functions and also provide user authentication. TFTP is a small and fast protocol that allows sending and receiving of files without user authentication. Due to this inherent security risk, it is not widely used. Trivial File Transfer Protocol (TFTP) uses the User Datagram Protocol (UDP) rather than the Transmission Control Protocol (TCP).

SMTP

It is the standard protocol for email services on a TCP/IP network and provides the ability to send and receive email messages. SMTP is an application layer protocol that enables the transmission and delivery of email over the Internet. The IETF created SMTP and they also maintain it.

The SMTP is also between two email servers to send and receive emails. However, the end client does not receive emails using SMTP. The end clients use the POP3 protocol to do that. SMTP is also known as RFC 821 and RFC 2821.

DNS

Every host in a network has a logical address called the IP address. These addresses are a bunch of numbers. When you go to a website such as https://networkustad.com  you are going to a host which has an IP address, but you do not have to remember the IP Address of every WebSite.

This is because Domain Name Service (DNS) helps map a name such as https://networkustad.com to the IP address of the host where the site resides. This makes it easier to find resources on a network. When you type in the address of a website in your browser, the system first sends out a DNS query to its DNS server to resolve the name to an IP address. Once the name is resolved, an HTTP session is established with the IP Address.

DHCP

Every host requires a logical address such as an IP address to communicate in a network. The host gets this logical address either by manual configuration or by a protocol such as DHCP. DHCP stands for Dynamic Host Configuration Protocol. It provides quick automatic, and central management for the distribution of IP addresses within a network.

To understand the importance of DHCP, imagine having to manage 10000 hosts in a network and assigning them IP addresses manually! Apart from the IP address, a host needs other information such as the address of the DNS server it needs to contact to resolve names, gateways, subnet masks, etc. We can use DHCP to provide all this information along with the IP address.

TCP

TCP stands for Transmission Control Protocol. It is the heart of the TCP/IP networks. The IP protocol deals only with packets, where the TCP enables two hosts to establish a connection and exchange streams of bits. TCP guarantees the delivery of data between hosts and also guarantees; the packet delivery order.

IP

IP stands for Internet protocol. It is the primary protocol in the Internet Layer of the Internet Protocol Suite. IP provides standard rules for sending and receiving data over the Internet. It allows devices running on different platforms to communicate with each other as long as they are connected to the Internet.

UDP

UDP Stands for “User Datagram Protocol”. The part of the TCP/IP suite of protocols used for data transferring. It is a “stateless” protocol because it does not provide any acknowledgment of the packet receiving at the receiving ends. UDP protocol is generally used for streaming media because of the low overheads.

It is simpler than TCP and lacks the flow-control and error-recovery functions of TCP. Thus, it uses fewer system resources. The difference between UDP and TCP is that UDP sends data without ack but TCP has ever required ack.

ICMP

ICMP is Stands for “Internet Control Message Protocol. It defines a small number of messages used for diagnostic and management purposes. Ping and traceroute also use ICMP. When information is transferred over the Internet; computer systems send and receive data using the TCP/IP protocol. If there is a problem with the connection; error and status messages regarding the connection are sent using ICMP, which is part of the Internet protocol.

SNMP

Simple Network Management Protocol (SNMP) is an application–layer protocol defined by the Internet Architecture Board (IAB) in RFC1157 for exchanging management information between network devices. SNMP is the part of Transmission Control Protocol⁄Internet Protocol (TCP⁄IP) protocol suite.

It is one of the widely accepted protocols to manage and monitor network elements. Most of the professional-grade network elements come with bundled SNMP agents. These agents have to be enabled and configured to communicate with the network management system (NMS).