June 2017
List and explain the significance of any 6 networking devices.
Different networking devices, work at different layers of the computer networks.
For example:
A LAN cable has got the purpose of connecting a computer to the local area network, a Wi-Fi router has got the purpose of sending and receiving data between you and your internet connection.
Different networking devices:
Network Hub:
Network Hub is a networking device which is used to connect multiple network hosts. A network hub is also used to do data transfer. The data is transferred in terms of packets on a computer network. So when a host sends a data packet to a network hub, the hub copies the data packet to all of its ports connected to. Like this, all the ports know about the data and the port for whom the packet is intended, claims the packet.
However, because of its working mechanism, a hub is not so secure and safe. Moreover, copying the data packets on all the interfaces or ports makes it slower and more congested which led to the use of network switch.
Network Switch:
Like a hub, a switch also works at the layer of LAN (Local Area Network) but you can say that a switch is more intelligent than a hub. While hub just does the work of data forwarding, a switch does ‘filter and forwarding’ which is a more intelligent way of dealing with the data packets.
So, when a packet is received at one of the interfaces of the switch, it filters the packet and sends only to the interface of the intended receiver. For this purpose, a switch also maintains a CAM (Content Addressable Memory) table and has its own system configuration and memory. CAM table is also called as forwarding table or forwarding information base (FIB).
Modem:
A Modem is somewhat a more interesting network device in our daily life. So if you have noticed around, you get an internet connection through a wire (there are different types of wires) to your house. This wire is used to carry our internet data outside to the internet world.
However, our computer generates binary data or digital data in forms of 1s and 0s and on the other hand, a wire carries an analog signal and that’s where a modem comes in.
A modem stands for (Modulator+Demodulator). That means it modulates and demodulates the signal between the digital data of a computer and the analog signal of a telephone line.
Network Router:
A router is a network device which is responsible for routing traffic from one to another network. These two networks could be a private company network to a public network. You can think of a router as a traffic police who directs different network traffic to different directions.
Bridge:
If a router connects two different types of networks, then a bridge connects two subnetworks as a part of the same network. You can think of two different labs or two different floors connected by a bridge.
Repeater:
A repeater is an electronic device that amplifies the signal it receives. In other terms, you can think of repeater as a device which receives a signal and retransmits it at a higher level or higher power so that the signal can cover longer distances.
For example, inside a college campus, the hostels might be far away from the main college where the ISP line comes in. If the college authority wants to pull a wire in between the hostels and main campus, they will have to use repeaters if the distance is much because different types of cables have limitations in terms of the distances they can carry the data for.
Study Strategy: Retrieval Practice
Different networking devices:
Network Hub:
Network Hub is a networking device which is used to connect multiple network _____. A network hub is also used to do _____ transfer. The data is transferred in terms of _____ on a computer network. So when a _____ sends a _____ to a network hub, the _____ copies the data packet to all of its _____ connected to. Like this, all the _____ know about the data and the port for whom the packet is intended, claims the packet.
However, because of its working mechanism, a hub is not so _____ and safe. Moreover, copying the data packets on all the interfaces or ports makes it _____ and more congested which led to the use of _____.
Network Switch:
Like a hub, a switch also works at the layer of _____ but you can say that a switch is more _____ than a hub. While hub just does the work of data forwarding, a switch does ‘_____’ which is a more intelligent way of dealing with the data packets.
So, when a packet is received at one of the _____ of the switch, it _____ the packet and sends only to the interface of the intended receiver. For this purpose, a switch also maintains a CAM (Content Addressable Memory) table and has its own system configuration and memory. CAM table is also called as forwarding table or forwarding information base (FIB).
Modem:
A Modem is somewhat a more interesting network device in our daily life. So if you have noticed around, you get an internet connection through a _____ (there are different types of wires) to your house. This wire is used to carry our internet data outside to the internet world.
However, our computer generates binary data or digital data in forms of _____ and on the other hand, a wire carries an _____ signal and that’s where a modem comes in.
A modem stands for (_____ + _____). That means it _____ and _____ the signal between the _____ data of a computer and the _____ signal of a telephone line.
Network Router:
A router is a network device which is responsible for _____ from one to another network. These two networks could be a private company network to a public network. You can think of a router as a _____ who directs different network traffic to different directions.
Bridge:
If a router connects two different types of networks, then a bridge connects two _____ as a part of the same network. You can think of two different labs or two different _____ connected by a bridge.
Repeater:
A repeater is an electronic device that _____ the signal it receives. In other terms, you can think of repeater as a device which receives a signal and retransmits it at a higher level or higher power so that the signal can cover _____ distances.
For example, inside a college campus, the hostels might be far away from the main college where the ISP line comes in. If the college authority wants to pull a wire in between the hostels and main campus, they will have to use repeaters if the distance is much because different types of cables have limitations in terms of the distances they can carry the data for.
Source: https://fossbytes.com/networking-devices-and-hardware-types/
File Permissions
There are three types of access restrictions:
Permission |
Action |
chmod option |
read |
(view) |
r or 4 |
write |
(edit) |
w or 2 |
execute |
(execute) |
x or 1 |
User Group Others
Symbolic rwx rw- r--
Binary 111 110 100
4+2+1 4+2+0 4+0+0
Octal 7 6 4
chmod with Letters
Usage: chmod {options} filename
Options |
Definition |
u |
owner |
g |
group |
o |
other |
a |
all (same as ugo) |
x |
execute |
w |
write |
r |
read |
+ |
add permission |
- |
remove permission |
= |
set permission |
First create some empty files
user@host:/home/user$ touch file1 file2 file3 file4 user@host:/home/user$ ls -l total 0 -rw-r--r-- 1 user user 0 Nov 19 20:13 file1 -rw-r--r-- 1 user user 0 Nov 19 20:13 file2 -rw-r--r-- 1 user user 0 Nov 19 20:13 file3 -rw-r--r-- 1 user user 0 Nov 19 20:13 file4
Add owner execute bit
user@host:/home/user$ chmod u+x file1 user@host:/home/user$ ls -l file1 -rwxr--r-- 1 user user 0 Nov 19 20:13 file1
Add other write & execute bit:
user@host:/home/user$ chmod o+wx file2 user@host:/home/user$ ls -l file2 -rw-r--rwx 1 user user 0 Nov 19 20:13 file2
Remove group read bit:
user@host:/home/user$ chmod g-r file3 user@host:/home/user$ ls -l file3 -rw----r-- 1 user user 0 Nov 19 20:13 file3
Add read, write and execute to everyone:
user@host:/home/user$ chmod ugo+rwx file4 user@host:/home/user$ ls -l file4 -rwxrwxrwx 1 user user 0 Nov 19 20:13 file4 user@host:/home/user$
Question 3: Domain Name Service
Domain Name Service (DNS)
Domain Name Service (DNS) is an Internet service that maps IP addresses and fully qualified domain names (FQDN) to one another. In this way, DNS alleviates the need to remember IP addresses. Computers that run DNS are called name servers. Ubuntu ships with BIND (Berkley Internet Naming Daemon), the most common program used for maintaining a name server on Linux.
Alternate Definition
The domain name system (DNS) is the way that internet domain names are located and translated into internet protocol (IP) addresses. The domain name system maps the name people use to locate a website to the IP address that a computer uses to locate a website. For example, if someone types TechTarget.com into a web browser, a server behind the scenes will map that name to the IP address 206.19.49.149.
Source: https://help.ubuntu.com/lts/serverguide/dns.html
Set DNS Servers:
You need to configure the /etc/network/interfaces file if you want to change your DNS server via the command line.
It should look something like this:
# The loopback network interface auto lo iface lo inet loopback # The primary network interface auto eth0 iface eth0 inet static address 192.168.X.X netmask 255.255.255.0 gateway 192.168.X.X dns-nameservers X.X.X.X
Study Strategy: Retrieval Practice
_____ (DNS)
_____ (DNS) is an Internet service that maps _____ and _____ (_____) to one another. In this way, DNS alleviates the need to _____ IP addresses. Computers that run DNS are called _____. Ubuntu ships with _____ (_____), the most common program used for maintaining a name server on Linux.
Set DNS Servers:
You need to configure the _____ file if you want to change your DNS server via the command line.
It should look something like this:
# The loopback network interface auto lo iface lo inet loopback # The primary network interface auto eth0 iface eth0 inet static _____ 192.168.X.X _____ 255.255.255.0 _____ 192.168.X.X _____ X.X.X.X
DNS—The Internet’s Directory Service
We human beings can be identified in many ways. For example, we can be identified by the names that appear on our birth certificates. We can be identified by our social security numbers. We can be identified by our driver’s license numbers. Although each of these identifiers can be used to identify people, within a given context one identifier may be more appropriate than another. For example, the computers at the IRS (the infamous tax-collecting agency in the United States) prefer to use fixed-length social security numbers rather than birth certificate names. On the other hand, ordinary people prefer the more mnemonic birth certificate names rather than social security numbers. (Indeed, can you imagine saying, “Hi. My name is 132-67-9875. Please meet my husband, 178-87-1146.”)
Just as humans can be identified in many ways, so too can Internet hosts. One identifier for a host is its hostname. Hostnames—such as cnn.com, www.yahoo. com, gaia.cs.umass.edu, and cis.poly.edu—are mnemonic and are therefore appreciated by humans. However, hostnames provide little, if any, information about the location within the Internet of the host. (A hostname such as www.eurecom.fr, which ends with the country code .fr, tells us that the host is probably in France, but doesn’t say much more.) Furthermore, because hostnames can consist of variable- length alphanumeric characters, they would be difficult to process by routers. For these reasons, hosts are also identified by so-called IP addresses.
An IP address consists of four bytes and has a rigid hierarchical structure. An IP address looks like 121.7.106.83, where each period separates one of the bytes expressed in decimal notation from 0 to 255. An IP address is hierarchical because as we scan the address from left to right, we obtain more and more specific information about where the host is located in the Internet (that is, within which network, in the network of networks). Similarly, when we scan a postal address from bottom to top, we obtain more and more specific information about where the addressee is located.
Services Provided by DNS
We have just seen that there are two ways to identify a host—by a hostname and by an IP address. People prefer the more mnemonic hostname identifier, while routers prefer fixed-length, hierarchically structured IP addresses. In order to reconcile these preferences, we need a directory service that translates hostnames to IP addresses. This is the main task of the Internet’s domain name system (DNS). The DNS is
(1) a distributed database implemented in a hierarchy of DNS servers, and (2) an application-layer protocol that allows hosts to query the distributed database.
The DNS servers are often UNIX machines running the Berkeley Internet Name Domain (BIND) software [BIND 2012]. The DNS protocol runs over UDP and uses port 53.
DNS is commonly employed by other application-layer protocols—including HTTP, SMTP, and FTP—to translate user-supplied hostnames to IP addresses. As an example, consider what happens when a browser (that is, an HTTP client), running on some user’s host, requests the URL www.someschool.edu/ index.html. In order for the user’s host to be able to send an HTTP request mes- sage to the Web server www.someschool.edu, the user’s host must first obtain the IP address of www.someschool.edu. This is done as follows.
- The same user machine runs the client side of the DNS application.
- The browser extracts the hostname, www.someschool.edu, from the URL and passes the hostname to the client side of the DNS application.
- The DNS client sends a query containing the hostname to a DNS server.
- The DNS client eventually receives a reply, which includes the IP address for the hostname.
- Once the browser receives the IP address from DNS, it can initiate a TCP connection to the HTTP server process located at port 80 at that IP address.
A Distributed, Hierarchical Database
In order to deal with the issue of scale, the DNS uses a large number of servers, organized in a hierarchical fashion and distributed around the world. No single DNS server has all of the mappings for all of the hosts in the Internet. Instead, the map- pings are distributed across the DNS servers. To a first approximation, there are three classes of DNS servers—root DNS servers, top-level domain (TLD) DNS servers, and authoritative DNS servers—organized in a hierarchy as shown in Fig- ure 2.19. To understand how these three classes of servers interact, suppose a DNS client wants to determine the IP address for the hostname www.amazon.com. To a first approximation, the following events will take place. The client first contacts one of the root servers, which returns IP addresses for TLD servers for the top-level domain com. The client then contacts one of these TLD servers, which returns the IP address of an authoritative server for amazon.com. Finally, the client contacts one of the authoritative servers for amazon.com, which returns the IP address for the hostname www.amazon.com.
Source(Book): Computer Networking, A Top-Down Approach
Study Strategy: Retrieval Practice
An IP address consists of _____ bytes and has a rigid hierarchical structure. An IP address looks like 121.7.106.83, where each period separates _____ of the bytes expressed in decimal notation from _____ to _____.
We have just seen that there are two ways to identify a host—by a _____ and by an _____. People prefer the more mnemonic _____ identifier, while routers prefer _____-length, _____ structured _____ addresses. In order to reconcile these preferences, we need a _____ service that translates hostnames to IP addresses. This is the main task of the Internet’s domain name system (DNS). The DNS is
(1) a _____ database implemented in a _____ of DNS servers, and (2) an application-layer protocol that allows hosts to query the distributed database.
The DNS servers are often UNIX machines running the _____ (BIND) software [BIND 2012]. The DNS protocol runs over UDP and uses port 53.
DNS is commonly employed by other application-layer protocols—including _____, SMTP, and FTP—to translate user-supplied hostnames to IP addresses. As an example, consider what happens when a browser (that is, an HTTP client), running on some user’s host, requests the URL www.someschool.edu/ index.html. In order for the user’s host to be able to send an HTTP request mes- sage to the Web server www.someschool.edu, the user’s host must first obtain the IP address of www.someschool.edu. This is done as follows.
- The same user machine runs the _____ side of the DNS application.
- The browser extracts the hostname, www.someschool.edu, from the URL and passes the hostname to the client side of the DNS application.
- The DNS client sends a query containing the hostname to a _____ _____.
- The DNS client eventually receives a _____, which includes the _____ address for the hostname.
- Once the browser receives the IP address from DNS, it can initiate a TCP connection to the HTTP server process located at port 80 at that IP address.
A Distributed, Hierarchical Database
In order to deal with the issue of scale, the DNS uses a large number of servers, organized in a hierarchical fashion and distributed around the world. No single DNS server has all of the _____ for all of the hosts in the Internet. Instead, the mappings are _____ across the DNS servers. To a first approximation, there are three classes of DNS servers—_____, _____ (_____) DNS servers, and _____ DNS servers—organized in a hierarchy as shown in Figure. To understand how these three classes of servers interact, suppose a DNS client wants to determine the IP address for the hostname www.amazon.com. To a first approximation, the following events will take place. The client first contacts one of the root servers, which returns _____ _____ for TLD servers for the top-level domain _____. The client then contacts one of these TLD servers, which returns the IP address of an _____ server for amazon.com. Finally, the client contacts one of the authoritative servers for amazon.com, which returns the _____ for the hostname www.amazon.com.
Distributed operating system
A computer operating system (OS) is one of the most important aspects of a computer. It is responsible for the underlying task management and orchestration of the computer's programs. A distributed operating system is a system that spreads the load over multiple computer hardware servers. This type of OS provides better performance and availability because it is distributed across multiple components.
Most operating systems are available in distributed versions. Some examples include UNIX®, Linux®, and the Windows® operating system. When the OS is distributed, it must be installed on multiple servers, which requires special configuration and management processes. This typically requires system engineers to manage the project.
A distributed OS is configured as a cluster of servers that share memory and tasks. These servers act in unison and provide more power than a single large computer server. This typically generates better performance because the load is distributed over multiple servers.
Grid computing is good example of distributed computing. This system uses computers connected to the Internet to complete complex tasks that require extensive processing power. Using a distributed model makes use of idle computer capacity because it shares multiple servers.
Computer capacity is known as the maximum available processing power of a computer system. It is typically calculated based on the available memory and computer processing units of the hardware platform. A distributed system provides additional capacity because it includes multiple servers.
There are specific algorithms used for a distributed operating system to handle task management. This arrangement is designed to process individual tasks on multiple servers based on priority and expected processing time. These algorithms vary in complexity, but are designed to make the best use of the available processing power from the shared servers.
A round-robin algorithm is an example of a simple algorithm that is used in a distributed operating system. This technique distributes incoming computer tasks to multiple servers based on a simple counting algorithm. Each task is assigned a specific number that corresponds to a specific server within the chain of available servers.
Some distributed operating system models monitor the available capacity of each server within the chain. This typically provides better performance than simple round-robin techniques because the server load is based on the actual available processing power. Advanced algorithms are more common in sophisticated multiprocessing operating systems.
Source: http://www.wisegeek.com/what-is-a-distributed-operating-system.htm
Study Strategy: Retrieval Practice
A computer operating system (OS) is one of the most important aspects of a computer. It is responsible for the underlying task management and orchestration of the computer's programs. A distributed operating system is a system that spreads the load over _____ computer hardware servers. This type of OS provides better _____ and _____ because it is distributed across multiple components.
Most operating systems are available in distributed versions. Some examples include UNIX®, Linux®, and the Windows® operating system. When the OS is distributed, it must be installed on multiple servers, which requires special configuration and management processes. This typically requires system engineers to manage the project.
A distributed OS is configured as a _____ of servers that share _____ and _____. These servers act in unison and provide more power than a single large computer server. This typically generates better performance because the load is distributed over multiple servers.
Grid computing is good example of distributed computing. This system uses computers connected to the Internet to complete complex tasks that require extensive processing power. Using a distributed model makes use of idle computer capacity because it shares multiple servers.
Computer capacity is known as the _____ of a computer system. It is typically calculated based on the available _____ and _____ of the hardware platform. A distributed system provides additional capacity because it includes multiple servers.
There are specific algorithms used for a distributed operating system to handle task management. This arrangement is designed to process individual tasks on multiple servers based on priority and expected processing time. These algorithms vary in complexity, but are designed to make the best use of the available processing power from the shared servers.
A _____ algorithm is an example of a simple algorithm that is used in a distributed operating system. This technique distributes incoming computer tasks to multiple servers based on a simple counting algorithm. Each task is assigned a specific number that corresponds to a specific server within the chain of available servers.
Some distributed operating system models monitor the available capacity of each server within the chain. This typically provides better performance than simple round-robin techniques because the server load is based on the actual available processing power. Advanced algorithms are more common in sophisticated multiprocessing operating systems.
Question:
Write a Linux shell script that will convert all numeric digits present in a text file into "*". The path of the text file would be given by the user.
Answer
#!/bin/bash echo "Enter the path filename" read filename echo "Entered name $filename" #Memory pie perl -p -i -e "s/\d/*/g" $filename
File Replication Service
File Replication Service (FRS) is a Microsoft Windows Server service for distributing shared files and Group Policy Objects.
NTFS
NTFS, an acronym that stands for New Technology File System, is a file system first introduced by Microsoft in 1993 with the release of Windows NT 3.1.
NTFS is the primary file system used in Microsoft's Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, Windows 2000, and Windows NT operating systems.
The Windows Server line of operating systems also primarily use NTFS.
FAT16, FAT32 and NTFS
File Allocation Table
FAT16 is the original file system used in DOS and Windows 3.x, and was originally only designed for use on relatively small partitions. It's been revised so that it's possible to make a FAT16 partition up to 4GB in size, but no more than that. FAT32 is a revised version of FAT16 that can be used to create much larger partitions and has native support for long filenames, and was introduced with Win98. Both FAT16 and FAT32 are also backwards- and cross-compatible with older versions of Windows and other OSes. However, both FAT16 and FAT32 suffer from many drawbacks: they have weak error recovery and no built-in file security, just to name two. NTFS, which was introduced with Windows NT, is much more secure and robust than FAT16 or FAT32, and offers better recovery from errors. NTFS is now offered on Windows 2000, Windows XP and Windows 2003 Server, although all of the above OS's can also use FAT16 or FAT32. It's generally recommended that NTFS be used except when backwards compatibility is urgently needed.
TFTP
TFTP stands for Trivial File Transfer Protocol. It's a technology for transferring files between network devices and is a simplified version of FTP (File Transfer Protocol).
TFTP was developed in the 1970s for computers lacking sufficient memory or disk space to provide full FTP support. Today, TFTP is also found on both consumer broadband routers and commercial network routers.
Home network administrators sometimes use TFTP to upgrade their router firmware, while professional administrators might also use TFTP to distribute software across corporate networks.
How TFTP Works Like FTP, TFTP uses client and server software to make connections between two devices. From a TFTP client, individual files can be copied (uploaded) to or downloaded from the server. In other words, the server is the one serving files while the client is the one requesting or sending them.
TFTP can also be used to remotely start a computer and back up network or router configuration files.
TFTP uses UDP for transporting data.
Source: https://www.lifewire.com/definition-of-tftp-817576
FTP
File Transfer Protocol (FTP) allows you to transfer copies of files between two computers using a simple network protocol based on Internet Protocol. FTP is also the term used when referring to the process of copying files using FTP technology.
History and How FTP Works
FTP was developed during the 1970s and 1980s to support file sharing on TCP/IP and older networks. The protocol follows the client-server model of communication. To transfer files with FTP, a user runs an FTP client program and initiates a connection to a remote computer running FTP server software. After the connection is established, the client can choose to send and/or receive copies of files, singly or in groups.
The original FTP clients were command line programs for Unix operating systems; Unix users ran 'ftp' command line client program to connect to FTP servers and either upload or download files. A variation of FTP called Trivial File Transfer Protocol (TFTP) was also developed to support low-end computer systems. TFTP provides the same basic support as FTP but with a simplified protocol and set of commands limited to the most common file transfer operations.Later, Windows FTP client software became popular as Microsoft Windows users preferred to have graphical interfaces to FTP systems.
An FTP server listens on TCP port 21 for incoming connection requests from FTP clients. The server uses this port to control the connection and opens a separate port for transferring file data.
Source: https://www.lifewire.com/file-transfer-protocol-817943
Study Strategy: Retrieval Practice
File Replication Service
File Replication Service (FRS) is a Microsoft Windows Server service for _____ and _____.
NTFS
NTFS, an acronym that stands for _____, is a file system first introduced by Microsoft in 1993 with the release of Windows NT 3.1.
NTFS is the primary file system used in Microsoft's Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, Windows 2000, and Windows NT operating systems.
The Windows Server line of operating systems also primarily use NTFS.
FAT16, FAT32 and NTFS
File Allocation Table
FAT16 is the original file system used in DOS and Windows 3.x, and was originally only designed for use on relatively _____ partitions. It's been revised so that it's possible to make a FAT16 partition up to 4GB in size, but no more than that. FAT32 is a revised version of FAT16 that can be used to create much larger partitions and has native support for _____, and was introduced with Win98. Both FAT16 and FAT32 are also backwards- and cross-compatible with older versions of Windows and other OSes. However, both FAT16 and FAT32 suffer from many drawbacks: they have weak error recovery and no built-in file security, just to name two. NTFS, which was introduced with Windows NT, is much more secure and robust than FAT16 or FAT32, and offers better recovery from errors. NTFS is now offered on Windows 2000, Windows XP and Windows 2003 Server, although all of the above OS's can also use FAT16 or FAT32. It's generally recommended that NTFS be used except when backwards compatibility is urgently needed.
TFTP
TFTP stands for Trivial File Transfer Protocol. It's a technology for transferring files between network devices and is a simplified version of FTP (File Transfer Protocol).
TFTP was developed in the 1970s for computers lacking sufficient memory or disk space to provide full FTP support. Today, TFTP is also found on both consumer broadband routers and commercial network routers.
Home network administrators sometimes use TFTP to upgrade their router firmware, while professional administrators might also use TFTP to distribute software across corporate networks.
How TFTP Works Like FTP, TFTP uses client and server software to make connections between two devices. From a TFTP client, individual files can be copied (uploaded) to or downloaded from the server. In other words, the server is the one serving files while the client is the one requesting or sending them.
TFTP can also be used to remotely start a computer and back up network or router configuration files.
TFTP uses UDP for transporting data.
Source: https://www.lifewire.com/definition-of-tftp-817576
FTP
File Transfer Protocol (FTP) allows you to transfer copies of files between two computers using a simple network protocol based on Internet Protocol. FTP is also the term used when referring to the process of copying files using FTP technology.
History and How FTP Works
FTP was developed during the 1970s and 1980s to support file sharing on TCP/IP and older networks. The protocol follows the client-server model of communication. To transfer files with FTP, a user runs an FTP client program and initiates a connection to a remote computer running FTP server software. After the connection is established, the client can choose to send and/or receive copies of files, singly or in groups.
The original FTP clients were command line programs for Unix operating systems; Unix users ran 'ftp' command line client program to connect to FTP servers and either upload or download files. A variation of FTP called Trivial File Transfer Protocol (TFTP) was also developed to support low-end computer systems. TFTP provides the same basic support as FTP but with a simplified protocol and set of commands limited to the most common file transfer operations.Later, Windows FTP client software became popular as Microsoft Windows users preferred to have graphical interfaces to FTP systems.
An FTP server listens on TCP port 21 for incoming connection requests from FTP clients. The server uses this port to control the connection and opens a separate port for transferring file data.
Source: https://www.lifewire.com/file-transfer-protocol-817943