Understanding Linux Server And Clients In Security

linux server and clients
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Understanding Linux Server And Clients In Security

An Introduction to Client-Server Communications

 

Servers are computers with the software installed that enables them to provide services to clients across the network. There are many types of services. Some provide external resources such as files, email messages, or web pages to clients upon request. Other services run maintenance tasks such as log management, memory management, disk scanning, and more. Each service requires separate server software. For example, the server in the figure uses file server software to provide clients with the ability to retrieve and submit files.

Client-server communications is discussed in more detail later in the course.

The image is a diagram that shows a server sending files to a client. Resources are stored on the server. A client is a hardware/software combination that people use directly. Files are downloaded from the server to the client.

Servers, Services, and Their Ports

In order that a computer can be the server for multiple services, ports are used. A port is a reserved network resource used by a service. A server is said to be “listening” on a port when it has associated itself with that port.

While the administrator can decide which port to use with any given service, many clients are configured to use a specific port by default. It is common practice to leave the service running in its default port. The table lists a few commonly used ports and their services. These are also called “well-known ports”.

Port Description
20/21 File Transfer Protocol (FTP)
22 Secure Shell (SSH)
23 Telnet remote login service
25 Simple Mail Transfer Protocol (SMTP)
53 Domain Name System (DNS)
67/68 Dynamic Host Configuration Protocol (DHCP)
69 Trivial File Transfer Protocol (TFTP)
80 Hypertext Transfer Protocol (HTTP)
110 Post Office Protocol version 3 (POP3)
123 Network Time Protocol (NTP)
143 Internet Message Access Protocol (IMAP)
161/162 Simple Network Management Protocol (SNMP)
443 HTTP Secure (HTTPS)

Ports and their uses in network communications are discussed in more detail later in the course.

Clients

Clients are programs or applications designed to communicate with a specific type of server. Also known as client applications, clients use a well-defined protocol to communicate with the server. Web browsers are web clients that are used to communicate with web servers through the Hyper Text Transfer Protocol (HTTP) on port 80. The File Transfer Protocol (FTP) client is software used to communicate with an FTP server. The figure shows a client uploading files to a server.

The image is a diagram that shows a client uploading files to a server. A client is a hardware/software combination that people use directly. Files are uploaded from the client to the server for storage. Resources are stored on the server.

About Adeniyi Salau 734 Articles
I am an IT enthusiast and a man of many parts. I am a Certified Digital Marketer, Project Manager and a Real Estate Consultant. I love writing because that's what keeps me going. I am running this blog to share what I know with others. I am also a Superlife Stem Cell Distributor. Our Stem Cell Products can cure many ailments.

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