Today we look more in detail about two link state routing protocols OSPF (Open shortest path first) and ISIS (Intermediate System to Intermediate System) dynamic routing protocol and similarities and key differences, OSPF vs ISIS, between both of them.

What is OSPF Dynamic Routing Protocol?

OSPF (Open shortest path first) is used in large enterprise networks. It collects link state information from routers in the network and determines the routing table information for packet forwarding. It creates a topology map of the network. OSPF exchanges routing information only when there is a change in network topology and it is best suited for complex networks which compromise multiple subnets by calculating shortest path effectively with minimum network traffic when change occurs.

Features of OSPF

• OSPF has complete visibility of network topology which let routers calculate best routes for all incoming requests

• There are no limitations on hop count, so it converges faster and has better load balancing

• It Multicasts link-state updates and sends the update only when there is a change in network 

What is ISIS Dynamic Routing Protocol? 

ANSI ISO developed an open standard and classless Interior gateway link state protocol named IS-IS (Intermediate System to Intermediate System). IS-IS uses Dijkstra SPF (shortest path first) algorithm to build IS-IS protocol databases to calculate the best path. It uses cost value for best path selection. It has fast convergence and large scalability. 

Features of ISIS dynamic routing protocol 

• Very fast convergence and large scalability
• Area structure is more flexible
• Extensible for both IPv4 and IPv6
• Scalability can be achieved with single area 

Commonalities between: OSPF & ISIS Dynamic Routing Protocols

• Both are link state routing protocols
• OSPF and IS-IS dynamic routing protocol uses Dijkstra SPF (Shortest Path First) algorithm
• OSPF and IS-IS dynamic routing protocol supports Variable length subnet mask (VLSM)
• Both are highly scalable protocols
• Both has highest convergence time after changes
• Both are open standard protocols
• Both have hierarchical structure (two hierarchy levels)
• Both support LANs and point-to-point protocols in same way
• Both use periodic Hello messages for establishment of neighbour 

Comparison Table: OSPF vs ISIS 

Let’s understand the differences between the two types of protocols in tabular form:

Download the comparison table: OSPF vs ISIS

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OSPF LSA TYPES

OSPF CHEATSHEET

]]> https://networkinterview.com/ospf-vs-isis/feed/ 0 3192 https://networkinterview.com/when-does-dns-use-tcp-or-udp/ https://networkinterview.com/when-does-dns-use-tcp-or-udp/#respond Wed, 14 Sep 2022 07:20:00 +0000 https://networkinterview.com/?p=13437 Introduction

There are quite is few services which may use both TCP and UDP protocol while communicating. The primary reason is based on type of request/response which needs to be furnished. Before we further drill into detail of protocol type used in DNS, lets have a quick run through TCP and UDP protocols.

What is TCP?

TCP is a connection-oriented protocol where the devices in communication should establish a connection before they can start with data transmission. The same stands true for termination of connection . Notable is that TCP is reliable and it guarantees delivery of data to the destination device.

What is UDP?

UDP is a connectionless protocol where there is no establishment of connection before data transmission. Further, there is no overhead related to opening, maintaining and terminating a connection. A key aspect of UDP is that delivery of data to the destination is not guaranteed.

While considering between UDP or TCP protocol for any application, another key aspect to note is that  UDP packets are smaller in size and cannot be greater then 512 bytes. Hence, any application needs where data to be transferred is greater than 512 bytes will require TCP protocol.

Example Scenario: When does DNS use TCP or UDP?

Lets take scenario of UDP protocol requirement in DNS – A Client queries for a record from DNS server. Even if the DNS server response is lost or becomes corrupt, its not a major challenge since client can ask for it again. Considering such use case, it is rational to use UDP when communicating with DNS for translation of domain name.

So, when does DNS use TCP? In order to maintain a consistent DNS database between DNS Servers. Hence, a transfer of DNS records (Zone transfer) between Primary and secondary DNS Servers is required which uses TCP protocol. The requirement here is that TCP, due to its reliability makes sure zone data is consistent across DNS servers. When a client doesn’t receive a response from DNS, it re-transmits the query using TCP after 3-5 seconds of interval.

Considering the above scenarios, it becomes essential that DNS server operators/providers must provide DNS service over both UDP and TCP. The same understanding stands true for network operators. We may encounter operational challenges when TCP protocol is blocked for communication of DNS service.

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TCP/IP MODEL vs OSI MODEL: Detailed Comparison

11 States of TCP Transition Explained

Are you preparing for your next interview?

Please check our e-store for e-book on DNS Interview Questions. All the e-books are in easy to understand PDF Format, explained with relevant Diagrams (where required) for better ease of understanding.

Today we look more in detail about two most popular and widely used reference models – OSI and TCP/IP, their features, functions and use cases.

About TCP/IP model

TCP stands for Transmission Control Program and IP stands for Internet protocol. TCP/IP model has a layered architecture and has four layers. The TCP/IP model is protocol-oriented standard. This model was developed by the Department of Defence (DOD) project agency. Internet protocols are a set of rules defined for communication over the network. TCP/IP is considered the standard model for networking and handles data transmission and IP handles addresses. The TCP/IP suite includes protocols such as TCP, UDP, ARP, DNS, HTTP, ICMP etc.

TCP/IP Model Features

• Multi-vendor support is available
• Used for around 35 years and most widely used protocol
• It supports interoperability
• It supports logical addressing
• It has routability feature
• It has name resolution feature
• Error control and flow control are supported features

About OSI Model

The OSI stands for Open System Interconnection, developed in the 1980s by the International standard organization.  It is a conceptual model used in network communication. The OSI model consists of seven layers and each layer is connected to each other. The data moves through the OSI model from its start till end (Last layer of OSI model).

OSI Model Features 

• Model to demonstrate how hardware and software work together
• Ease of troubleshooting (Each layer detects and handles error) 
• Reduction in complexity
• Standardization of interfaces
• Facilitates modular engineering
• Provides interoperability between vendors 

The application layer of the TCP/IP model maps to the first three layers i.e., Application, Presentation & Session Layer of the OSI model. The transport layer maps directly to the transport layer of the OSI model. The Internet layer maps to the Network layer of the OSI model. The last two layers of the OSI model map to the Data link layer and physical layer of OSI model. TCP/IP model is more widely used as compared to OSI model. 

Similarities between TCP/IP and OSI Model

Common Architecture – both models are logical and have similar architecture based on layered approach.

Defined Standards – both models define the standard and framework for implementing the standards and devices. 

Troubleshooting is simplified – by breaking complex functions at each layer into simple components.

Pre-defined standard – the protocols and standards are already pre-defined; and models do not redefine them, it just references it or uses it. Like Ethernet standards were already defined by IEEE before the origin of this model and it uses this in its reference at Physical layer or Network access layer.

Similar functionality at transport and network layer – function performed between presentation and network layer is similar to the function performed at transport layer.

Comparison Table: TCP/IP MODEL vs OSI MODEL

Below table summarizes the differences between the two:

FUNCTION	TCP/IP MODEL	OSI MODEL
Definition	TCP/IP stands for Transmission control protocol/ Internet protocol	OSI stands for Open systems Interconnection
Developed by	It is developed by DOD (Department of Defence) project agency.	OSI model is developed by ISO (International standard organization).
Technology/ Platform	It comprises of a set of standard protocols which lead to development of the Internet. It is a communication medium which provides connection between hosts.	It is an independent standard and generic protocol used as a communication gateway between network and end user.
Delivery of Packets	No guaranteed delivery of packets at transport layer.	Transport layer provides guaranteed delivery of packets.
Approach	Based on horizontal approach.	Based on vertical approach.
Application Layer	Session and presentation layers are not separate, both are included in application layer.	Session and presentation layers are separate
Type of  Model	Implemented model of OSI model.	It is a reference model on which various networks are built.
Network layer	Network layer provides only connectionless service.	Network layer provides connection oriented and connection less services (Both)
Replaceable/ Non-replaceable Protocols	Protocols can’t be easily replaceable	In OSI model protocols are hidden and can be easily replaceable when technology changes occur
Number of Layers	Comprises of four layers	It comprises of seven layers
Protocol Dependent/Independent	Services, protocols, and interfaces are not properly segregated but are protocol dependent	Services, protocols and interfaces are defined and it is protocol independent
Usage	Widely used model	Limited usage of the model
Standardization of devices	Do not provide standardization of devices	Standardization of devices like router, switches, load balancers and other hardware devices

Download the Comparison Table: TCP/IP MODEL vs OSI MODEL

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OSI Model – The 7 Layers

Introduction to TCP/IP

Today we look more in detail about how TCP/IP offers reliable transmission using 3-way handshake, how TCP 3-way handshake works, its features etc.

What is TCP 3-Way Handshake?

TCP/IP protocol operates at the network layer in OSI stack. TCP/IP model which is derived before OSI model dictates how TCP/IP communication works.

TCP/IP has several characteristics as under:

• It supports flexible TCP/IP architecture
• It is easy to add more systems to network 
• The network remains intact until source and destination machines are working in proper manner
• TCP is a connection-oriented protocol
• It offers reliability and ensure that data which arrives out of sequence should be put back to order
• TCP allows to implement flow control to ensure sender never overloads receiver with data 

TCP/IP provides reliable communication with Positive Acknowledgement and Retransmission (PAR). The Protocol data unit (PDU) of transport layer also known as segment. A device using PAR resends the data until it is acknowledged. If a data unit is found damaged at the receiver end, then the segment is discarded. Sender has to resend the data unit for positive acknowledgement 

How does TCP 3-way handshake (SYN, SYN + ACK, ACK) work?

Since TCP is a connection-oriented protocol a connection is mandate to be established before two devices start communication. TCP uses a process of three-way handshake to negotiate the sequence and acknowledgement fields to initiate a session. The graphical representation of process is as under:

• The three-way handshake starts with Host A initiates connection by sending the TCP SYN packet to the destination host. The packet contains a random sequence number (e.g., 1234) which indicates the beginning of the sequence number of data that host A will be transmitting.
• The server receives the packet and responds with his own sequence number. This response also includes the acknowledgement number which is increment of host A sequence number by ‘1’ 
• Host A acknowledges the server response by sending acknowledgement number which is server sequence number incremented by ‘1’. Once they establish a reliable connection, actual data transfer start.

Once the data transmission process is completed. TCP will terminate the connection between two devices. This is a four-step process as outlined below.

• The client application who wants to close connection send a TCP segment with the FIN flag set as ‘1’
• The server receives the TCP segment and acknowledge it will ACK
• Server sends its own TCP segment with FIN flag set to ‘1’ to client to terminate connection
• The client acknowledges the server FIN segment and connection is closed.

Continue Reading:

11 States of TCP Transition Explained

HTTP vs TCP : Detailed Comparison

The IPv6 is the abbreviation for the Internet Protocol version 6. The IPv6 is the most updated protocol of network layer which can make the transmission of data possible in packets between two networks. It simply means that one can easily send in and also receive data on the network in packet form. Just for our reference, Ipv6 address are basically categorized into 3 types –

• Unicast : represent a single interface.
• Anycast : represent a set of interfaces, where a packet sent to an anycast address which is a member of the set. Anycast addresses are used for load-balancing.
• Multicast : represents a dynamic group of hosts. In this addressing type, packets are sent to all interfaces that are part of a multicast group

IPv6 protocol was laid down by the IETF– Internet Engineering Task Force well before in time, i.e.  1998, the specification for which is RFC 2460. The extent to which the IPv6 will be able to serve is rightfully considered to be the upcoming generation of the Internet. This protocol has the ability to serve extensively large scale organizations. Back in 2004, Korea and Japan first came up and announced having publicly assigned IPv6. The Internet Protocol Version 6 is the latest protocol version which surpasses and fixes up the limitations of its predecessor internet Protocol Version 4.

Related – IPv4 vs IPv6

Features of IPv6

The key features of IPv6 are:

Address space

To let the subsidiary internets of the large organizations be deployed and to ultimately enable the subnetting, IPv6 has been designed to accommodate larger address space. 128-bits can be possible which makes it up to 16-bytes in the IP address which can possibly have combinations over approximately 3.4×1038 addresses.

Due to a larger possibility of more number of addresses available, the need for conserving the address won’t stand necessary.

Header Format

The header format of version 6 of Internet Protocol is optimized to include the optional and the non-essential fields under the extension headers which come into the sight after the Internet Protocol v 6 header. Both the formats of version 4 and 6 are not directly compatible and for being able to process both, the router must implement both the formats. The version 4 header is twice as small as the version 6 header format.

Address Configuration

The version 6 of the Internet Protocol can configure the addresses both in the absence and the presence of a DHCP server (Dynamic Host Configuration Protocol), which simply means that both stateless and stateful address configurations are supported, respectively.

In the absence, the link local address is configured automatically by the hosts with IpPv6 addresses.

Security

This protocol for IPSec needs some support which for fulfilling the security needs of the network provides a solution based on the standards. This will also assist in interoperations of the protocol implementations.

Routing Infrastructure and Hierarchical Address

The routing infrastructure of the version 6 protocol enables hierarchical addressing system which is more efficient. The hierarchy is formed based on the occurrences of the service providers of the internet.

Connectivity

The connectivity of the hosts to the internet has been enhanced more wherein every unique IP address can directly connect to any other host over the internet though being constrained by the policies of the organization or through firewalls with the IPv6.

Node Interaction

The communication of neighboring nodes in the version 6 internet protocol is managed by a sequence of Internet Control Messages. This neighbor discovery procedure is the new replacement to the Address Resolution Protocol, ICMPv4 redirecting messages and ICMPv4 router discovery which were based on broadcasting with the more competent Neighbor Discovery messages both for one-to-one communication or multicasted, i.e. one-to-many communication.

Support for QoS

The quality of service is taken care of by the IPSec encryption of packet payload in this Internet protocol version. There are new segments or fields incorporated in the header section of the protocol to be able to recognize and manage the traffic. For being able to recognize the traffic, a header field of Flow Label is added which enables the router to spot and endow it with the respective flow of packets to keep the packets communication between the source or host and the receiver. And for enhancing the quality of service, there is even no problem in the flow of packets even if it is IPSec encrypted.

Extension

While the IPv4 can only support up to 40 bytes of address choices or options, for expanding the IPv6 header, the extension headers can be added. The extension header size of IPv6 can be of the size of the IPv6 packet. Simply put, more information can be added in the extension headers.

Related – IPv6 Stateless Autoconfiguration

Error control process tracks data frames that got lost or corrupted during transmission. The Data link layer follows a technique to retransmit frames to detect or identify transit errors and also take actions which are required to reduce or eliminate such errors. 

In this article we will learn more about a technique used at Data link layer protocols known as Automation Repeat Request (ARQ) to make an effort to detect loss of packets during transmission, its advantages and how it is performed.  

What is ARQ (Automatic Repeat Request)?

There are two ways of doing error control namely error detection and error correction. Error detection simply means detection or identification of error. These errors may cause the receiver to receive garbled or unclear or distorted messages. Error correction means correction or fixing errors. Reconstruction and rebuilding of original data which is error free. 

The main function of ARQ protocol is send receives an acknowledgement from the receiver end suggesting that the frame or packet is received correctly before timeout is occurred, timeout defines a specific time window within which acknowledgement has to be sent by the receiver to the sender.

If timeout happens sender will not get acknowledgement within specific time, which implies that data packet or frame is either lost or got corrupted during its transmission hence sender will re-transmit the data frame or packet and ARQ protocol will ensure that process will be repeated until the right packet transmission is completed.  

Techniques of Error Control

There are various techniques of error control such as:

Stop and Wait ARQ –

It is also known as alternating bit protocol. It is the simplest flow and error control mechanism. This is usually required in telecommunications to transmit data or information between two connected devices. Receiver signals its readiness to receive data for each frame, sender sends information or data packet to receiver. Sender will stop and wait for acknowledgement from the receiver.

If acknowledgement is not received within a fixed time frame, the sender will resend the data frame and wait for acknowledgement. If the sender receives acknowledgement, it will send the next data frame and wait again. And this process will keep on repeating until send has left with no data frame or information to send to the receiver. 

Sliding Window ARQ –

It is used for continuous transmission error control and it is categorized into Go Back N ARQ and Selective repeat ARQ. 

Go Back N ARQ –

It sends frames within a specified window frame even without receiving acknowledgement.

Selective Repeat ARQ –

Only suspected or damaged or lost data frames are retransmitted. Sender only retransmits frames for which No acknowledgement is received. It is used however lesser because of more complexity at sender and receiver end as each packet must be acknowledged individually. 

Applications of Automatic Repeat Request

ARQ protocols have a wide range of applications to ensure they provide reliable transmissions over unreliable upstream sources. These protocols operate on short wave radio so as to ensure reliable delivery of signals.  

For the same function of ARQ, there are various applications: 

• Transmission Control Protocol (TCP)
• Specific Service Orientation Protocol: Error-correction of message signals in ATM networks
• High-Level Data Link protocol (HLDL)
• IBM Binary synchronous Communications Protocol (IBSC) 
• Xmodem : modem file transfer protocol

Pros and Cons of Automatic Repeat Request

PROS

• Quite simple error detection and error correction techniques
• Simple decoding equipment as compared to other techniques
• ARQ is adaptive, as information is retransmitted only if error occurs 
• Ideal for using noisy channels
• It has both error flow and error control mechanism 
• It has timer implementation 

CONS

• High error rate on a medium and channel could cause too much transmission of the frames or packets of information
• High error rate in channel could lead to loss of information and lead to reduction in efficiency or productivity of the system 
• System throughput is lowered by ARQ when channel error is high 

Continue Reading:

What is HSRP (Hot Standby Router Protocol) ?

What is NETCONF protocol?

What is MPLS and how is it different from IP Routing?

There are several data programming and configuration protocols that make the flow of information seamless across the networks. Among these protocols, OpenFlow and Netconf are considered to be popular and widely used ones when it comes to software defined networking (SDN).

Let’s see what these two popular protocols have to offer when we make a comparison OpenFlow vs Netconf on the grounds of various features.

Introduction

 When you are seeking for a specialized protocol that can program the forwarding tables situated within a switch then OpenFlow is put into use. On the other hand, Netconf is more flexible in nature and can be applied for any kind of configuration. It is especially beneficial when you are seeking for a protocol that is not dependent on the data type in order to deliver a successful configuration.

OpenFlow vs Netconf: The Protocol Comparison

 We have created a detailed table down below to help you understand how these two protocols are identical or distinct from one another on the grounds of certain critical parameters.

Conclusion

From the above table defining the features of both the protocols, it is pretty clear that both OpenFlow and Netconf have their own significant place when we analyse their roles in a software defined network.

From the points defined above in OpenFlow vs Netconf table, many would prefer to with an OpenFlow protocol (as the only setback that one can find is with the state of entries, where the entries are temporary in nature) and there is nothing wrong in that. But when we look from the viewpoint of the vendors and the device makers, then we would find that they would prefer a restricted standardized process for their own good. It has been explained in the table with the help of an example as well.

Both the protocols have their own pros and cons and they have been well evaluated above. Now, it is totally up to the users, what are the features that they give utmost priority and take the services of either of the SDN protocols discussed above accordingly.

Related – Enabling and Configuring NETCONF

SSH (or Secure Shell) is a protocol that facilitates secure communications between two systems using a client/server architecture and allows users to connect to a host remotely. Unlike other remote communication protocols such as FTP or Telnet, SSH encrypts the connection session, making it impossible for someone to obtain unencrypted passwords.

SSH is designed to replace older and less secure methods to register remotely on another system through the command shell, such as telnet or ssh. A related program, the SCP, replaces other programs designed to copy files between hosts such as RCP. Since these old applications do not encrypt passwords between the client and the server, avoid using them as long as possible. The use of secure methods to register remotely to other systems reduces security risks for both the client system and the remote system.

SSH FEATURES

SSH protocol provides the following types of protection:

• After the initial connection, the client can verify that it is connecting to the same server to which it was previously connected.
• The client transmits its authentication information to the server using a robust 128-bit encryption.
• All data sent and received during the session is transferred through 128-bit encryption, which makes it extremely difficult to decrypt and read.
• The client can forward X11 applications from the server. This technique, called X11 forwarding, provides a secure means to use graphic applications over a network.

Since the SSH protocol encrypts everything it sends and receives, it can be used to secure insecure protocols. The SSH server can become a conduit to make insecure protocols secure by using a technique called port forwarding, such as POP, by increasing the security of the system in general and data.

Red Hat Enterprise Linux contains the general OpenSSH package (OpenSSH) as well as the OpenSSH server (OpenSSH-server) and client (OpenSSH-clients) packages.

WHY USE SSH?

Users have a variety of tools at their disposal that allows them to intercept and redirect network traffic to gain access to the system. In general terms, these threats can be cataloged as follows:

Interception of communication between two systems – In this scenario, there is a third party somewhere in the network between entities in communication that makes a copy of the information that passes between them. The interceptor may intercept and retain the information, or may modify the information and then send it to the recipient to which it was intended.

• This attack can be mounted through the use of a sniffer package – a very common network utility.
• The personification of a particular host – With this strategy, an interceptor system pretends to be the recipient to whom a message is intended. If the strategy works, the user’s system does not realize the deception and continues communication with the wrong host.

This occurs with techniques such as DNS poisoning or IP spoofing (IP address deception).

Both techniques intercept potentially confidential information and if this interception is done for hostile purposes, the result can be catastrophic.

ENCRYPTION TECHNIQUES

The significant advantage offered by SSH over its predecessors is the use of encryption to ensure the secure transfer of information between the host and the client. Device refers to the remote server you are trying to access, while the client is the computer you are using to access the host. There are three different encryption technologies used by SSH:

• Symmetric encryption
• Asymmetric encryption
• Hashing

SYMMETRIC ENCRYPTION

Symmetric encryption is a form of encryption in which a secret key is used for both encryption and decryption of a message, both by the client and by the host. Indeed, anyone who has the key can decrypt the message that is transferred.

Symmetric encryption is often called a shared key or shared secret encryption. Normally there is only one key that is used, or sometimes a pair of keys where one key can be easily calculated with the other key.

Symmetric keys are used to encrypt all communication during an SSH session. Both the client and the server derive the secret key using an agreed method, and the resulting key is never disclosed to third parties. The process of creating a symmetric key is carried out using a key exchange algorithm.

ASYMMETRIC ENCRYPTION

Unlike symmetric encryption, asymmetric encryption uses two separate keys for encryption and decryption. These two keys are known as the public key and the private key. Together, these keys form the public-private key pair.

The public key, as the name suggests, is openly distributed and shared with all parties. While it is closely linked to the private key in terms of functionality, the private key cannot be calculated mathematically from the public key. The relationship between the two keys is highly complex: a message encrypted by the public key of a machine can only be decrypted by the same private key of the machine. This unidirectional relationship means that the public key cannot decrypt its messages or decrypt anything encrypted by the private key.

The private key must remain private, that is, for the connection to be secure, no third party should know it. The strength of the entire connection lies in the fact that the private key is never revealed since it is the only component capable of decrypting messages that were encrypted using its public key. Therefore, any party with the ability to decrypt publicly signed messages must possess the corresponding private key.

Unlike general perception, asymmetric encryption is not used to encrypt the entire SSH session. Instead, it is only used during the symmetric encryption key exchange algorithm. Before initiating a secure connection, both parties generate temporary public-private key pairs and share their respective private keys to produce the shared secret key.

The similar technique to this is the CSMA/CD. The only difference is that, in the CSMA CD, the collision is detected whereas here we will try to avoid the collision and send the data directly without any interruptions. In the CSMA/CD, the transmission is only handled if there is a collision detected whereas it takes no actions.

Whereas in the CSMA/CA, the protocol will first check the path prior to the collision and try to avoid any collisions before it occurs. This technique will consume more data as well as will use ore amount of network traffic. This is because the protocol will first check the path by sending dummy data before it actually sends the original data. Hence, more data and network traffic are consumed.

In short, the main aim of this technique is to ensure that the data is transmitted safely and the collision is avoided. There are proper steps taken to ensure that the data does not collide. There are three main types of techniques used for collision avoidance.

Techniques:

There are 3 techniques that we can use for collision avoidance:

1. Interframe space
2. Contention window
3. Acknowledgments

Interframe Space (IFS)

In this technique, when the channel or the medium is found idle, sender does not directly transmit the data. Instead, it will wait for a fixed amount of time called interframe space. When the previously transmitted signal will reach the previous station, it will then send the next data. During the IFS, the sent data will reach either one of the stations. If the IFS time is over and the channel is still idle, the next data is sent. In this way, there are not collision faced.

Contention windows

Contention windows will decide the time amount into various this technique is similar to the p-persistent method. The only difference is that here the random outcome will define the time slots. A number of slots are not fixed, it will completely depend on the binary exponential strategy. After the time slot is completed, when the channel is found idle, the data is transferred. A time slot will double each time whenever the station is not able to detect any of idle channel.

When the channel is found busy, the process isn’t restarted instead it will restart the timer and follow entire process again.

Acknowledgment

Besides all the measures taken for not avoiding collisions, there are still some chances where the data might collude. In such cases, Acknowledgment is used. The receiver will send Acknowledgement saying that the data is received. Once the data is received, it is confirmed that the data is not destroyed.

Working:

CDMA protocol working is simple. The main aim is to avoid the collision and send the data without any issues. Station will first of all check the line and see if it is idle or not. If the line is idle, it will wait for a certain amount of time. The IFS is the estimated time for the time required by the data to travel the channel.

Once, the timer is over, it will send the frame. In this way, there is last amount of chance of the collision and hence this technique is called collision avoidance technique.

If the line is found busy, the timer won’t continue instead it will restart the timer and wait for a certain amount of time again until the line is cleared.

Therefore, it is one of the best ways to send the data with least chances of a collision.

Advantages:

• There is least amount of collision and hence there are no to very fewer chances of data destruction.
• The three-technique will ensure the best level of safety and techniques to avoid the collision.
• Our data is safe and won’t corrupt while transiting data

Disadvantages:

• Time taken for data transfer is more as it will wait for a certain amount of time whenever any data is to be sent.
• The data consumption is more as there is dummy data sent to check if the frame is idle or not.

There are different ports for each of the protocols and the addresses out there, these can contain up to 16-bit of space. These are basically just the unsigned numbers and the number is called a port number .The port number range from values of 0 to 65535.

Different kind of protocols use a port number, the two most popular protocol that is using port number are

• TCP (Transmission Control Protocol)
• UDP (User Datagram Protocol)

All port numbers are directly associated with one of the IP addresses of the host as well as there is one or more protocol that it follows for the data transmissions.  A port number is used to get the final destination or the origin of the network for any particular message received. In this way, the message or the packet that is arrived is forwarded to their own destination using the port number. Therefore, for all these usages, it is necessary to have a port number when transferring data using any of the networks. Below is an example scenario where Client with IP address 1.1.1.1 and port number 5000 needs to communicate with Web server, which has IP address 1.1.1.2 and port number 80. Generally communication with Web server is on HTTP with TCP protocol.

Handling and Managing the port numbers

As we have seen above, the port number is managed by the operating system or the network itself. The point is who controls the global DNS route and the port number. These are controlled by IANA (Internet signed Numbers Authority). IANA also controls all the other things such as IP Address, DNS, port number, etc for mostly all internet services.

There are three kinds of the port number

• Well known ports
• Registered Ports
• Dynamic or commonly known as private ports

Well, known ports are already defined for specific purposes and already defined by the system. Therefore, it is also called System port. One can use these ports but the rules to use these ports are different and it is hard implementing these for different usage. The range includes from 0 t 1023.

In other words, one might not be able to define the port number in these series. Most of the people who are working with any kind of network will know most of these port number and the usage. In this way, they can use any port number easily for the given purpose.

Well known common port number

These are some of the common port numbers that are sued for specific services. These can be different but in most of the cases, these are the port number used.

• 20: File Transfer Protocol (FTP) used in Data Transfer
• 21: File Transfer Protocol (FTP) used in Command Control
• 22: Secure Shell (SSH) to make sure login in secure
• 23: Telnet remote login service that is used for decrypting text messages
• 25: Simple Mail Transfer Protocol (SMTP) used for E-mail routing
• 53: Domain Name System (DNS) service
• 80: Hypertext Transfer Protocol (HTTP) mostly used in the World Wide Web
• 110: Post Office Protocol (POP3)
• 119: Network News Transfer Protocol (NNTP)
• 123: Network Time Protocol (NTP)
• 143: Internet Message Access Protocol (IMAP) Management of digital mail
• 161: Simple Network Management Protocol (SNMP)
• 194: Internet Relay Chat (IRC)
• 443: HTTP Secure (HTTPS) HTTP over TLS/SSL

Port scanning

Port scanning is the procedure to scan all the ports available in the system or any network. There are various tools available that will give me information for any specific ports. Port scanning is done in order to ensure that the network is working properly without any issues. If there is a port that is not catching enough signals, there are chances that something might be wrong with the network or the system.

Moreover, port scanning has much other uses such as it is used for security purpose when there is an attack. Sometimes, there might be more than one service that uses the same port number, one can use the port scanning technique to make sure that the port number they want to use is free or one can know which process or service is using that particular port number.

Telnet is often referred to as TN. It was first conceived back in 1969, by the IETF (Internet Engineering Task Force).  Telnet stands for the Teletype Network.

Telnet is especially designed for remote server access where we can manage all the client/server architectures. There are also other commands that we need to insert in order to successfully complete the Telnet operation. Device must be supported for the commands in order to use Telnet. There might be some devices that are not supported and hence we can’t execute the command in those devices.

Working

Telnet basically sends all the messages in plain and clear text. It means there is no specific mechanism for security. Therefore, it is not considered that secured and people don’t prefer sending their personal data over telnet. This is one of the biggest disadvantage we see in the Telnet. Moreover, there is no proper authentication required. In other words, we can’t ensure that data is just transferred between two of the host and there is no interception in the middle. Therefore, this is another problem that is happening when it comes to the security of the Telnet.

However, now in many services and applications, there are improved measures taken in order to make it more secure. Therefore, there are many applications where the Secure Shell (SSH) is replacing Telnet.

Telnet Clients

There are many clients available for Telnet utility. Some of them are as follows –

• Putty and Plink – These both are the free and the open source SSH clients that can be used. They both are compatible with the Raw TCP clients for Windows, Unix, as well as for the Linux.
• There is another client called AbsoluteTelnet available for the windows. Here, we will also find the SSH and SFTP support.
• Rumba is the terminal emulator for the Telnet.

These are some of the clients we may like to use. However, we will also need the support of the libraries in order to transmit the data, which brings us to the next topic.

Telnet Libraries

There are many telnet libraries where the client and the server are supported. In some of the libraries, the security is not maintained.

Here are some of the famous libraries used and related information –

Go-telnet: In this library, the client and the server support is available. Along with this, the security is also taken care of and we can use TELNET for the data transmission.

Libtelnet: Here, we can use it for client and server. However, security is not maintained here. The license of this library is in the Public domain.

Telnetlib: Here, the only client is supported and we won’t get the support for the security or the server.

All the libraries are available on all the platforms. Hence, we can use this library on BSD, GNU Linux, Windows, and also on Mac OS. Therefore, we can use the libraries according to the requirements. The programming language is different here. However, most of the people are using the Go-telnet as most of the things are supported and people also want security over their data.

Related – SSH vs Telnet

SMTP is used by everyone indirectly when they send and receive any emails using any of the service providers. Even the private emails and the service based email use the same protocol. This protocol is maintained by IETF which stands for Internet Engineering Task Force, the protocol was even created by the same team.

For technical understanding, some people also call it RFC 821 and RFC 2821. However, it is widely popular by the name SMTP. After 2008, people also used to call it RFC 5321 and later on the name SMTP came.

All the famous email services such as Gmail, Yahoo, Microsoft, Outlook, etc uses SMTP.

The SMTP can be used in the TCP and is generally used under port number 25.

Components

SMTP can be segregated into 4 main components. The four main components are –

• MUA – Stands for Mail User Agent
• MSA – Stands for the Mail Submission Agent
• MTA – Stands for the Mail Transfer Agent
• MDA – Stands for the Mail Delivery Agent

If you are wondering what are these names, then the

• MUA means the sender and the one who initiates the email.
• MSA and the MTA are the two services that will submit and transfer your email to the receiver.
• MDA is the receiver.

Working

When the MUA sends a mail to anyone on the internet, It first falls into the MSA which further processes it. The MSA uses SMTP on port 587. Most of the mail service provider will allow mail to be sent from the port 25.

When the MSA gets the mail, it will then transfer the email to the MTA. Here, various things are checked such as DNS and the MX record. Once everything is confirmed, the mail is transferred and delivered to the receiver ie MDA. Various things are verified when the mail reaches MSA .Here all the necessary information is checked and the IMAP and the POP are used in order to send the email to the receiver.

Once everything is done, the receiver will receive the email. All of these things are done in the fraction of seconds. For this reason, whenever you send an email to anyone, the email gets delivered in minimal amount of time and the receiver can open it.

Please note that various spam checks and all the other services that you get in the email service are done after the email reaches the receiver. These things are not handled by the protocol.

Data in SMTP

You might be wondering about the commands or the data that are stored in the SMTP. Here, the three main types of command are stored, they are

MAIL: This is called the return path. Here, the return address is established

RCPT: It is command used to delivery the receipt of the email success or the failure to the sender. There are two receipts generated total for each of the recipients.

DATA: This is the actual data in the email. The one that you are sending and have created. There is also a header present in the DATA itself where all the information is stored. Whereas the body part is written differently.

Also refer NTP

NTP is the protocol used in reference to time. NTP is responsible for synchronizing the time of the computer with the time of the network. NTP stands for Network Time Protocol.

It is one of the oldest protocols used and is related to TCP/IP protocol. It is generally used on the client-server programs that are running on all the computers.

History

Talking about the history of the NTP, it was first discovered back in 1981 in the University of Delaware. The protocol was designed to be fault tolerant and easily scalable. It was developed by David Mills.

Working

If you wondering how the NTP protocol works, it is pretty simple and clear. First of all, the NTP sends a time-request with the server. When the request is received by the server, the server will then calculate the delay between time of clock in the computer and the network timing. Once the difference between the local offset and the computer is found, the NTP protocol will adjust the computer’s timing accordingly.

In other words, it will then match the clock of the computer with the network timing. There are approximately six changes required in order to set the clock. NTP takes more time in completing its process in comparison to other protocols. We might see that it will take around 5 to 10 minutes for setting the clock which is a bit high. This is only for the first time when the clock is synced. Once, the sync is done, the timing is way faster.

However, there are more benefits to the time it takes. Once the clock is set, it checks the clock after every 10 minutes. The clock is updated and simultaneously only one message exchange is required by NTP. This is the process of NTP client-server synchronization. The transaction occurs over UDP protocol (User Datagram Porocotol) on the port 123. Moreover, peer clocks can also be synchronized using this protocol.

Advantages and features

These are several advantages or features that we can get from NTP as enlisted below –

• Many people have access to atomic clocks and GPS clocks with the help of NTP.
• Manual configuration of clock on every machine is very tedious, time consuming and error prone activity. NTP circumvents such issues and requires minimal management overhead.
• NTP has the UTC (Coordinated Universal Time) to set the clock and the sync the clock of your computer. Therefore, we will get the exact timing that you want without any failure.
• There are almost no downtime or single errors when you are using NTP. Also, when we are using it in the local area network, there is no time taken. Clock can be synced in hardly a second. Therefore, it is one of the fastest ways here.
• The best part about NTP being so fast is due to the reason that NTP does not perform the calculations when it comes to the local time. Instead, the machine does all of this operation making it a lot faster as compared to protocols.

Final words

Many people think that they don’t require NTP. However, it is required as even if there is a slight change seen between the network time and the local computer time, there might be many mechanisms and the works that will be delayed , especially system logs and event details.

Continue Reading:

What is SMTP

Introduction to TCP/IP

TCP vs UDP

Here’s a detailed comparison:

1. Connection Handling

• TCP: Connection-oriented. Establishes a connection (3-way handshake: SYN, SYN-ACK, ACK) before data transfer and terminates it (FIN/ACK) afterward.
• UDP: Connectionless. No handshake; data is sent immediately without setup.

2. Reliability

• TCP: Reliable. Guarantees delivery using acknowledgments (ACKs), retransmissions, and error checking.
• UDP: Unreliable. No ACKs, retransmissions, or guarantees of delivery.

3. Ordering

• TCP: Ensures in-order delivery using sequence numbers.
• UDP: No ordering; packets may arrive out of order.

4. Speed & Efficiency

• TCP: Slower due to connection setup, acknowledgments, and retransmissions.
• UDP: Faster and lighter, with minimal overhead.

5. Flow & Congestion Control

• TCP: Adjusts transmission rate dynamically to avoid network congestion.
• UDP: No congestion control; can flood the network.

6. Header Size

• TCP: Larger header (20-60 bytes) with fields for sequencing, ACKs, and control flags.
• UDP: Smaller header (8 bytes) with only source/destination ports, length, and checksum.

7. Use Cases

• TCP:
  • Web browsing (HTTP/HTTPS)
  • Email (SMTP, IMAP)
  • File transfer (FTP)
  • Secure shell (SSH)
  • Database communication
  • Any application needing reliability.
• UDP:
  • Video streaming (e.g., YouTube, Netflix)
  • VoIP (e.g., Skype, Zoom)
  • Online gaming (e.g., Fortnite, Call of Duty)
  • DNS queries
  • Live broadcasts (e.g., Twitch)
  • IoT sensors (where speed > reliability).

8. Error Checking

• TCP: Full error detection and correction via checksums and retransmissions.
• UDP: Basic checksum for error detection (no correction).

9. Multicast/Broadcast Support

• TCP: Only unicast (one-to-one).
• UDP: Supports unicast, multicast (one-to-many), and broadcast (one-to-all).

10. Examples in Networking

• TCP:

HTTP (Port 80)

HTTPS (Port 443)

FTP (Port 21)

SSH (Port 22

• UDP:

DNS (Port 53)

DHCP (Ports 67, 68)

QUIC (Used in HTTP/3)

SNMP (Port 161)

Difference between TCP and UDP

Below table summarizes the difference between UDP and TCP:

When to Use Which?

• Use TCP when data integrity and reliability are critical (e.g., file downloads, emails).
• Use UDP when speed and low latency matter more than reliability (e.g., live video, gaming).

Through UDP a source host send messages to destination host with a minimum of protocol mechanism. Further as UDP is transaction oriented,so delivery and duplicate protection are not guaranteed. UDP is generally used in video conferencing and real-time computer games. The protocol permits individual packets to be dropped and UDP packets to be received in a different order than that in which they were sent, allowing for better performance.

Related – TCP vs UDP

Related – TCP HEADER

(Transmission Control Protocol )

Source port (16 bits): Port related to the application in progress on the source machine

Destination port (16 bits): Port related to the application in progress on the destination machine

Sequence number (32 bits): When the SYN flag is set to 0, the sequence number is that of the first word of the current segment. When SYN is set to 1, the sequence number is equal to the initial sequence number used to synchronize the sequence numbers (ISN)

Acknowledgement number (32 bits): Also called the acquittal number relates to the sequence number of the last segment expected and not the number of the last segment received.

Data offset (4 bits): This makes it possible to locate the start of the data in the packet. Here, the offset is vital because the option field is a variable size

Reserved (6 bits): A currently unused field but provided for future use

Flags (6×1 bit): The flags represent additional information: •URG: if this flag is set to 1 the packet must be processed urgently

ACK: if this flag is set to 1 the packet is an acknowledgement.

PSH (PUSH): if this flag is set to 1 the packet operates according to the PUSH method.

RST: if this flag is set to 1 the connection is reset.

SYN: The TCP SYN flag indicates a request to establish a connection.

FIN: if this flag is set to 1 the connection is interrupted.

Window (16 bits): Field making it possible to know the number of bytes that the recipient wants to receive without acknowledgement

Checksum (CRC): The checksum is conducted by taking the sum of the header data field, so as to be able to check the integrity of the header

Urgent pointer (16 bits): Indicates the sequence number after which information becomes urgent

Options (variable size): Various options

Padding: Space remaining after the options is padded with zeros to have a length which is a multiple of 32 bits

Continue Reading:

 UDP HEADER

 TCP vs UDP