Difference between File Transfer Protocol (FTP) and Secure File Transfer Protocol (SFTP)

FTP stands for File Transfer Protocol. It is a protocol which is used to transfer or copies the file from one host to another host. But there may be some problems like different file name and different file directory while sending and receiving file in different hosts or systems. And in FTP, secure channel is not provided to transfer the files between the hosts or systems. It is used in port no-21.

SFTP stands for Secure File Transfer Protocol. It is a protocol which provides the secure channel, to transfer or copies the file from one host to another host or systems. SFTP establishes the control connection under SSH protocol and It is used in port no-22.

There are some difference between them which are given below:

FTP	SFTP
It stands for File Transfer Protocol.	It stands for Secure File Transfer Protocol.
In FTP, secure channel is not provided to transfer the files between the hosts.	In SFTP, secure channel is provided to transfer the files between the hosts.
It is a part of TCP/IP protocol.	It is a SSH protocol.
It usually runs on port no-21.	It runs on port no-22.
It establishes the connection under TCP protocol.	It establishes the control connection under SSH protocol.
It does not encrypt the data before sending.	It encrypted data before sending.
It works on direct method for file transfer.	It works on tunelling method for transferring of files.
It makes uploading and downloading of files without any security.	It maintains full security of the data by using SSH keys.

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What is Local Host?

When you call an IP address on your computer, you try to contact another computer on the internet but when you call the IP address 127.0.0.1 then you are communicating with the localhost. Localhost is always your own computer. Your computer is talking to itself when you call the localhost. Your computer not always directly identifies the local host. Within your personal network localhost has a separate IP address like 192.168.0.1.(for most cases) which is different to the one you use on the internet. This is usually dynamically assigned by the internet service provider (ISP). Localhost can be seen as a server that is used on your own computer.

This term is generally used in the context of networks. Localhost is not just the name for the virtual server but it is also its domain name. Just like .example, .test, or .invalid, ., .localhost is a top-level domain reserved for documentation and testing purposes. While accessing the domain, a loopback is triggered. If you access “http://localhost” in the browser, the request will not be forwarded to the internet through the router. It will instead remain in your own system. Localhost has the IP address 127.0.0.1. This refers back to your own server.

127.0.0.1 – how does loopback work?

To communicate with each other within a network IP addresses are used. The participants in the network has their own unique address. Using TCP/IP data packets are able to reach the correct destination. The protocol pair Transmission Control Protocol (TCP) and Internet Protocol (IP) are some of the main features of the internet. TCP/IP is also used outside of the internet in local networks. The Internet Protocol is responsible for allowing the IP address and subnet mask to address subscribers in a network during the transmission.

The allocation of public IP addresses is regulated by an international organization which is the Internet Corporation for Assigned Names and Numbers (ICANN). ICANN is also responsible for the allocation of domain names called the Domain Name System (DNS). But certain address ranges are reserved for special purposes, like the range from 127.0.0.0 to 127.255.255.255. There is no reliable information on why that range was chosen. IP addresses on the internet are divided into different classes. The first class Class A started with 0.0.0.0 (reserved address) and ended with 127.255.255.255. 127 is the last block of the Class A network. Its important position could have been the reason for its selection.

Within this address range a Localnet can be set up. The special thing about this range is that IP addresses are not uniquely assigned in it, as is usually the case. Also it was reserved by ICANN.

If you enter an IP address or corresponding domain name in your browser, the router forwards your request to the internet which corrects you to the server. This means that if you enter 172.217.0.0, you will reach the Google homepage but the situation is different with 127.0.0.1. The requests to this address will not be forwarded to the internet. TCP/IP recognizes from the first block (127) that you don’t want to access the internet, you are calling yourself instead. This then triggers the loopback.

The reason why loopback device is created so that the back link to your own computer works. Through the operating system this is a virtual interface that is created. The interface is called lo or lo0 and can also be displayed using the ifconfig command in Unix systems. A similar command for Windows is ipconfig.

What is localhost used for?

Developers use the local host to test web applications and programs. Network administrators use the loopback to test network connections. Another use for the localhost is the hosts file, where you can use the loopback to block malicious websites.

For Testing Purposes –

Web servers mainly use the local host for the programming applications that need to communicate over the internet. During development, it is important to find out whether the application actually works as developed once it has internet access. Localhosts’ other functions are only possible if the required files can be found on the internet. As we can see that there is a difference between opening a HTML document on your PC or loading it onto a server and accessing it. Releasing a product without testing it doesn’t make sense. So loopback is used by developers to test them. They can stimulate a connection while also avoiding the network errors. The connection just stays completely inside their own system.

Another advantage of using localhost for testing purposes is the speed. Usually more than 100 milliseconds are taken when you send a request over the internet. The maximum transmission time is just one millisecond for sending a ping to localhost. The correctness of the internet protocol can also be implemented using this technology.

If you want to set up your own test server on your PC to address it through the localhost, right softwares are needed. Softwares such as XAMPP specifically designed for use as a localhost can be used.

To block websites –

Localhost can also block the hosts files. This file is a predecessor of the Domain Name System (DNS). In this IP addresses can be assigned to the corresponding domains. The domain name is translated into an IP address when you enter a website address in the browser. It used to be the host file, but today usually the global DNS is used but the host file is still present in most operating systems. In Windows, the file is found under \system32\drivers\etc\hosts where as with macOS and other Unix systems, it is found under /etc/hosts.

There are probably these two entries left if there are no file changes done:

 127.0.0.1       localhost

 ::1             localhost 

The name resolution for the localhost need not have to be done over the internet. Localhost can also use the host file to block certain websites. For this, the website to be blocked must be entered into the list and the IP address 127.0.0.1 must be assigned to the domain. If you or a malicious script try to call up the locked domain, the browser will check the hosts file first and will find your entry there. The domain name 0.0.0.0 can also be used.

The browser will then try to access the corresponding website on the server with 127.0.0.1. However, it is unlikely that the browser will be able to locate it, as the requested file will not be there. However, if your own test server is set up, then the browser may find home.html, which is just your own file. An error message appears instead of the requested website if you have not set up your own test server. Ad inserts throughout the system can be switched off using this technology. To avoid every entry manually, you can find finished and regularly extended host files on the Internet.

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DNS Look-Up

Prerequisite – Domain Name System (DNS)

Need of DNS:

There are 232 IP Addresses (approximately 4, 294, 967, 296). With growth of internet at a rapid pace came issue of remembering websites with their IP Address (not an issue if superhuman or bot pretending to be human). This issue was resolved using DNS. Domain Name System is method of resolving human-understandable URLs into their respective IP addresses. While you enter URL (this URL is known as FQDN – Fully Qualified Domain Name) into browser, DNS takes care of looking at actual IP address associated with website.

DNS Look-Up:

To resolve such DNS queries, there are Domain Name Servers built across world that takes your DNS look-up request and resolve it. There are 5 types of Name Servers –

1. Caching Name Servers.

2. Recursive Name Servers.

3. Root Name Servers.

4. Top Level Domain (TLD) Name Servers.

5. Authorative Name Servers.

Caching and Recursive Name Servers are generally provided by Internet Service Providers. Purpose of Caching Name Server is to store known domain names for certain amount of time (similar to caching in data storage). Recursive Name Server performs Full Name Resolution. There are 13 Root Name Servers across globe, responsible for directing requests to appropriate TLD Server.

Figure – DNS Look-up

◉ When you type FQDN in your browser, it checks host files already available in your system. A host file has entries as follows –

<IP-Address> <Domain-name>

Example –

127.0.0.1 localhost

216.58.203.36 www.google.com

◉ If the IP Address is not found in Host files, then DNS look-up is carried to Caching Name Server, which stores domain names for certain amount of time.

◉ If caching name server does not resolve look-up, it is then transmitted to Recursive Name Server. Recursive name servers are responsible to perform full DNS Resolution requests.

◉ The request from Recursive Name Server is transmitted to 13 Root Name Servers using Anycast (It is technique that is used to route traffic to different destinations depending on factors like location, link health and congestion).

◉ Root Name Server responds to DNS Look-up with name of TLD Name Server that should be queried.

◉ For each Top Level Domain in Domain Name (A top-level domain is part of domain that comes after the dot, for example, com, org or net) there is Top Level Domain (TLD) Name Server. TLD server responds to DNS Look-up with redirect, informing your system about which Authorative Name Server to contact.

◉ Finally, DNS Look-up is redirected to Authorative Name Server for resolving website name and it provides actual IP Address of the server.

This strict hierarchy maintains stability of internet by resolving every lookup in correct manner. This protects against malicious redirecting traffic. Nowadays devices have built-in local cache servers to prevent performing DNS lookup for every new TCP connection.

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Why HTTP is not Secure ?

Well everyone of us at least once come across the statement:

“Make sure abc website uses HTTPS before entering your private information.”

If yes then have you ever tried to find the reason behind this statement. Let’s find out the reason.

Before proceeding further two points must be clear-

1. HTTP :

HyperText Transfer Protocol (HTTP) is the core communication protocol used to access the World Wide Web.

It uses a message-based model in which a client sends a request message and server returns a response message.

2. HTTPS :

HyperText Transfer Protocol Secure (HTTPS) clearly it names indicate that this is an secure advancement of HTTP. It is basically the same application-layer protocol as HTTP but it is tunneled over secure transport mechanism.

The point to understand is that HTTP transfer data as plain text whereas HTTPS adds a encryption layer to data.

Now we have understand that HTTP does not encrypt our data while communication which means a attacker which is suitably positioned on the network can eavesdrop or look our data.

Let’s dive deeper!

To start our exploration we are using Linux machine and wireshark as packet analyzer tool (they are used for network analysis).

Firstly we have to setup wireshark to monitor all ongoing HTTP traffic for that we will enter the

following filter in wireshark to only get HTTP requests:

http && ip.addr == "ip address" 

Now, we are able to monitor all ongoing traffic as shown in image:

You might be thinking that an attacker is only able to see your browsing but he can also get your credentials if victim try to login let’s see now visit a page and enter the credentials let say username =’test’ and password=’test’ then press login.When we switch back to wireshark and find that corresponding request we are able to see our entered username and password.

But, if we try to analyze packets for HTTPS request it doesn’t disclose any credentials due to encryption.

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Difference between Internet and WWW

1. Internet:

The internet is a globally connected network system facilitating worldwide communication and access to data resources through a huge collection of personal, public, business, academic and government networks. it’s governed by agencies just like Internet Assigned Numbers Authority (or IANA) that establish universal protocols.

2. World Wide Web (WWW):

World Wide Web (WWW), byname Web, is leading information retrieval service of web (the worldwide computer network). Online gives users access to a huge array of documents that are connected to every other by means of hypertext or hypermedia links—i.e., hyperlinks, electronic connections that link related pieces of data so as to permit a user quick access to them. Hypertext allows the user to pick a word or phrase from text and thereby access other documents that contain additional information concerning that word or phrase.

Difference between Internet and WWW :

INTERNET	WWW
Internet is a global network of networks.	WWW stands for World wide Web.
Internet is a means of connecting a computer to any other computer anywhere in the world.	World Wide Web which is a collection of information which is accessed via the Internet.
Internet is infrastructure.	WWW is service on top of that infrastructure.
Internet can be viewed as a big book-store.	Web can be viewed as collection of books on that store.
At some advanced level, to understand we can think of the Internet as hardware.	At some advanced level, to understand we can think of the WWW as software.
Internet is primarily hardware-based.	WWW is more software-oriented as compared to the Internet.
It is originated sometimes in late 1960s.	English scientist Tim Berners-Lee invented the World Wide Web in 1989.
Internet is superset of WWW.	WWW is a subset of the Internet.
The first version of the Internet was known as ARPANET.	In the beginning WWW was known as NSFNET.
Internet uses IP address.	WWW uses HTTP.

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Difference between HTTP and HTTPS

1. HyperText Transfer Protocol (HTTP) :

HyperText Transfer Protocol (HTTP) is a protocol using which hypertext is transferred over the Web. Due to its simplicity, http has been the most widely used protocol for data transfer over the Web but the data (i.e. hypertext) exchanged using http isn’t as secure as we would like it to be. In fact, hyper-text exchanged using http goes as plain text i.e. anyone between the browser and server can read it relatively easy if one intercepts this exchange of data.

2. Hypertext Transfer Protocol Secure (HTTPS) :

Hypertext Transfer Protocol Secure (HTTPS) is an extension of the Hypertext Transfer Protocol (HTTP). It is used for secure communication. In HTTPS, the communication protocol is encrypted using Transport Layer Security.

Difference between HTTP and HTTPs:

HTTP	HTTPS
HTTP stands for HyperText Transfer Protocol.	HTTPS for HyperText Transfer Protocol Secure.
In HTTP, URL begins with “http://”.	In HTTPs, URL starts with “https://”.
HTTP uses port number 80 for communication.	HTTPs uses 443 port number for communication.
HTTP is considered to be unsecure.	HTTPs is considered as secure.
HTTP works at Application Layer.	HTTPS works at Transport Layer.
In HTTP, Encryption is absent.	Encryption is present in HTTPS.
HTTP does not require any certificates.	HTTPS needs SSL Certificates.

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Types of DNS Attacks and Tactics for Security

Prerequisite – Domain Name Server, DNS Spoofing or DNS Cache poisoning

Domain Name Server is a prominent building block of the Internet. It’s developed as a system to convert alphabetical names into IP addresses, allowing users to access websites and exchange e-mails. DNS is organized into a tree-like infrastructure where the first level contains topmost domains, such as .com and .org. The second level nodes contain general, traditional domain names. The ‘leaf’ nodes on this tree are known as hosts.

DNS works similar to a database which is accessed by millions of computer systems in trying to identify which address is most likely to solve a user’s query.

In DNS attacks, hackers will sometimes target the servers which contain the domain names. In other cases, these attackers will try to determine vulnerabilities within the system itself and exploit them for their own good.

Types of Attacks:

1. Denial of service (DoS) –

An attack where the attacker renders a computer useless (inaccessible) to the user by making a resource unavailable or by flooding the system with traffic.

2. Distributed denial of service (DDoS) –

The attacker controls an overwhelming amount of computers (hundreds or thousands) in order to spread malware and flood the victim’s computer with unnecessary and overloading traffic. Eventually, unable to harness the power necessary to handle the intensive processing, the systems will overload and crash.

3. DNS spoofing (also known as DNS cache poisoning) –

Attacker will drive the traffic away from real DNS servers and redirect them to a “pirate” server, unbeknownst to the users. This may cause in the corruption/theft of a user’s personal data.

4. Fast flux –

An attacker will typically spoof his IP address while performing an attack. Fast flux is a technique to constantly change location-based data in order to hide where exactly the attack is coming from. This will mask the attacker’s real location, giving him the time needed to exploit the attack. Flux can be single or double or of any other variant. A single flux changes address of the web server while double flux changes both the address of web server and names of DNS serves.

5. Reflected attacks –

Attackers will send thousands of queries while spoofing their own IP address and using the victim’s source address. When these queries are answered, they will all be redirected to the victim himself.

6. Reflective amplification DoS –

When the size of the answer is considerably larger than the query itself, a flux is triggered, causing an amplification effect. This generally uses the same method as a reflected attack, but this attack will overwhelm the user’s system’s infrastructure further.

Measures against DNS attacks:

1. Use digital signatures and certificates to authenticate sessions in order to protect private data.

2. Update regularly and use the latest software versions, such as BIND. BIND is an open source software that resolves DNS queries for users. It is widely used by a good majority of the DNS servers on the Internet.

3. Install appropriate patches and fix faulty bugs regularly.

4. Replicate data in a few other servers, so that if data is corrupted/lost in one server, it can be recovered from the others. This could also prevent single point failure.

5. Block redundant queries in order to prevent spoofing.

6. Limit the number of possible queries.

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Introduction of Active Directory Domain Services

A directory is a hierarchical structure that stores information about objects on the network. A directory, in the most generic sense, is a comprehensive listing of objects. A phone book is a type of directory that stores information about people, businesses, and government organizations. Phone books typically record names, addresses, and phone numbers.

Active Directory (AD) is a Microsoft technology used to manage computers and other devices on a network. It is a primary feature of Windows Server, an operating system that runs both local and Internet-based servers.

Benefits of Active Directory –

◉ Hierarchical organizational structure.

◉ Multimaster Authentication & Multimaster replication (the ability to access and modify AD DS from multiple points of administration)

◉ A single point of access to network resources.

◉ Ability to create trust relationships with external networks running previous versions of Active Directory and even Unix.

Directory Service –

A directory service is a hierarchical arrangement of objects which are structured in a way that makes access easy. However, functioning as a locator service is not AD’s exclusive purpose. It also helps organizations have a central administration over all the activities carried out in their networks. Essentially a Network Directory Service:

◉ Provides information about the user objects, computers and services in the network.

◉ Stores this information in a secure database and provides tools to manage and search the directory.

◉ Allows to manage the user accounts and resources, apply policies consistently as needed by an organization.

Active Directory provides several different services, which fall under the umbrella of “Active Directory Domain Services, ” or AD DS. These services include:

1. Domain Services –

Stores centralized data and manages communication between users and domains; includes login authentication and search functionality

2. Certificate Services –

It generates, manages and shares certificates. A certificate uses encryption to enable a user to exchange information over the internet securely with a public key.

3. Lightweight Directory Services –

Supports directory-enabled applications using the open (LDAP) protocol.

4. Directory Federation Services –

Provides single-sign-on (SSO) to authenticate a user in multiple web applications in a single session.

5. Rights Management –

It controls information rights and management. AD RMS encrypts content, such as email or Word documents, on a server to limit access.

Domain Controllers –

A server that is running AD DS is called a domain controller.Domain controllers host and replicate the directory service database inside the forest. The directory service also provides services for managing and authenticating resources in the forest.These servers host essential services in AD DS, including the following:

– Kerberos Key Distribution Center (kdc)

– NetLogon (Netlogon)

– Windows Time (W32time)

– Intersite Messaging (IsmServ)

Active Directory Objects:

1. Container Objects –

These objects can contain other objects inside them, and we can make collection from them. For Ex- Forest, Tree, Domains, Organisational Units.

2. Leaf Objects –

These objects can not contain other objects inside them. For Ex- users, computers, printers, etc.

Common Terminologies and Active Directory Concepts:

◉ Schema –

A set of rules, the schema, that defines the classes of objects and attributes contained in the directory, the constraints and limits on instances of these objects, and the format of their names.

◉ Global catalog –

A global catalog that contains information about every object in the directory. This allows users and administrators to find directory information regardless of which domain in the directory actually contains the data. For more information about the global catalog, see The role of the global catalog.

◉ Forest Root Domain –

The first domain that is installed in an Active Directory Forest is referred to as the root domain.

◉ Sites –

Sites in AD DS represent the physical structure, or topology, of your network. AD DS uses network topology information, which is stored in the directory as site, subnet, and site link objects, to build

the most efficient replication topology.

◉ Lightweight Directory Access Protocol –

AD is based on the Lightweight Directory Access Protocol (LDAP). This protocol provides a common language for clients and servers to speak to one another.

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Domain Resolution and URL Processing

A domain name is an address that is used to access any website. Domain Name is unique in nature and it is very easy to remember. By typing the Domain Name user can reach the website whichever he desires. The actual address of any website is very complicated but with the help of Domain Name, this complicated address can be converted into a simplified human-comprehensible form. Domain Name is formed with the help of rules and procedures of DNS.

Why Domain Name is Important ?

The domain name is easy to remember but the IP address is not. Let’s take an example of the telephone directory, we don’t remember the phone number of the persons we just remember the name of the person and then search the number using their names, not with their phone numbers. An IP address can be changed in the back-end but the domain name remains the same.

History: We are using the Human Comprehensible form of the host’s numerical address since the ARPANET era. Earlier each computer on the network used to retrieve host files from the computer at SRI which used to map computer host names to numerical addresses. As networking started to grow rapidly henceforth it became nearly impossible to perform the task with traditional methods and therefore in 1983, the Domain Name System was introduced on the ARPANET.

Characteristics:

◉ The shorter the domain name then it’s easier to remember and understand and the longer the Domain Name it’s hard to remember and understand therefore keeping Domain Name short and crisp is advisable.

◉ Domain Name should be easy to spell because the user won’t be able to remember it correctly if it’s complicated.

◉ In Domain Name .com extension is most popular as many people remember the sites with this extension and tend to forget other extensions.

◉ Sometimes Domain Name will not have any meaning but it becomes so popular that people recognize that domain name just by listening to its name, so we can also create a brand, and we don’t really need any meaning unless and until Domain Name becomes a brand.

◉ Domain Name ideally should not contain hyphen and numbers as it becomes cumbersome to remember.

Steps for Domain Resolution and URL Processing: 

When we type a web address into a web browser, our computer needs to convert them into an IP address. So that it can contact our web server and delivers to you. This is called a forward lookup because we are converting a hostname into an IP address. It is also called a reverse lookup when we are converting an IP address into a hostname.

◉ First, we will type the name of the website which we want to access. For example — facebook.com.

◉ Then this domain name will map into their corresponding IP address, and the conversion of the domain name to IP address is the responsibility of the resolver. There is a resolver between request and root server.

◉ The website request first goes to the root server, it can be done by 2 methods either with a recursive method or with the iterative method. There are a total of 13 root servers all over the world.

◉ The resolver then gives an IP address of the next level to the resolver. The next level consists of generic servers or country servers.

◉ The resolver resolves the domain name from right to left means in our example it will first resolve “.com”. Then “.com” gives a link to the resolver after that our request will be forwarded to the Authoritative Server.

◉ Authoritative Servers stores all the IP addresses and names. There can be multiple IP addresses of a particular website. Facebook has more than 70 thousand servers hence the IP address can be multiple.

◉ This IP address is given to the resolver and then the resolver gives that IP address to our computer. Then we can access the data in our computer.

These steps are only performed when we access any website for the very first time. When we access that website a second time then our request is not forwarded to the root server because our internet service provider(ISP) cached that IP address so that whenever you need to access that website, it will provide IP address easily.

Advantages:

◉ Good Domain Name adds credibility also it separates from other Domain Names.

◉ Also, Domain Name gives visibility to the brand and it also attracts many users.

◉ Domain Name can increase search engine ranking once it becomes popular among Internet Users.

◉ Domain Name establishes a unique identity in cyberspace.

◉ Domain Name can be resold, leased, and bartered which is also one of the great advantages.

Disadvantages:

◉ DNS registry can only be controlled by ICANN which is a big challenge as it’s tied to only one country and henceforth it also challenges Net Neutrality.

◉ In DNS server-side only see the IP address and henceforth it can be manipulated by hackers.

◉ Also, the DNS server is based on the slave-master relationship which is another challenge.

◉ In case the host starts malfunctioning then it becomes hard to access the web page.

◉ In many instances, the hacker’s target server machine and makes the user redirect to another webpage which results in phishing.

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Difference between Domain and Workgroup

1. Domain :

Domain is a client/server network where user can login from any device of the office. Also known as Remote login. It has a centralized administration and all devices can be managed from a centralized device. It prefers a centralized storage and all the users data is stored at a centralized storage device which can be NAS or SAN.

2. Workgroup :

Workgroup is a peer to peer windows computer network, where users can use his login credentials only on his or her system and not others. It holds an distributed administration wherein each user can manage his machine independently. Most storage is distributed. Each device has its own dedicated storage.

Difference between Domain and Workgroup :

DOMAIN	WORKGROUP
The computers in a domain have a centralized database.	The computers in workgroup mainly has its own local database.
A domain is mainly to transfer and share sensitive and important data only.	A Workgroup is used to share less secure and personal data only due to less security.
A domain is mainly preferred for large public and business networks.	A workgroup is mainly preferred for small local area networks like schools, colleges, buildings, etc.
A domain is used to transfer and share sensitive and important data due to security.	A workgroup is used to share personal data as it is less secure.
A domain can work better for large numbers of devices.	A workgroup works better for fewer computers.
The domain names are provided by domain controller on the basis of IP address.	In workgroup there is no dependencies on any hardware components and server for assigning the name.
Data can be recovered in a domain from the centralized storage.	Data recovery is not possible in a workgroup due to the local storage of each device.
A Domain can be formed using the devices of one or more different networks domain and adding all the intended devices to it.	The devices of the same network can only be added to a workgroup.

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Dynamic Domain Name System (DDNS) in Application Layer

When DNS (Domain Name System) was designed, nobody expected that there would be so many address changes such as adding a new host, removing a host, or changing an IP address. When there is a change, the change must be made to the DNS master file which needs a lot of manual updating and it must be updated dynamically.

Dynamic Domain Name System (DDNS):

It is a method of automatically updating a name server in the Domain Name Server (DNS), often in real-time, with the active DDNS configuration of its configured hostnames, addresses, or other information. In DDNS, when a binding between a name and an address is determined, the information is sent, usually by DHCP (Dynamic Host Configuration Protocol) to a primary DNS server.

The primary server updates the zone. The secondary servers are notified either actively or passively. Inactive notification, the primary server sends a message to secondary servers, whereas, in the passive notification, the secondary servers periodically check for any changes. In either case, after being notified about the change, the secondary requests information about the entire zone (zone transfer).

DDNS can use an authentication mechanism to provide security and prevent unauthorized changes in DNS records.

Advantages:

1. It saves time required by static addresses updates manually when network configuration changes.

2. It saves space as the number of addresses are used as required at one time rather than using one for all the possible users of the IP address.

3. It is very comfortable for users point of view as any IP address changes will not affect any of their activities.

4. It does not affect accessibility as changed IP addresses are configured automatically against URL’s.

Disadvantages:

1. It is less reliable due to lack of static IP addresses and domain name mappings.

2. Dynamic DNS services alone can not make any guarantee about the device you are attempting to connect is actually your own.

Uses:

1. It is used for Internet access devices such as routers.

2. It is used for for security appliance manufacturers and even required for IP-based security appliances like DVRs.

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