Chapter 10

Client server Model

By Nikhila Sattala
October 12, 2021

The client-server model is a fundamental concept in networking that forms the basis for many networked applications and services. It is a versatile and widely adopted architecture in networking and distributed computing.


  • A client is a computer or device that requests and uses services, resources, or data from another computer or device called the server.
  • Clients initiate communication by sending requests to servers and wait for responses.
  • Clients can be software applications running on end-user devices such as laptops, smartphones, or desktop computers.
  • Typical client applications include web browsers, email clients, file transfer programs, and more.


  • A server is a computer or device that provides services, resources, or data to clients.
  • Servers wait for incoming requests from clients, process these requests, and send back the appropriate responses.
  • Servers are often specialized hardware or software designed to perform specific tasks, such as web servers, email servers, file servers, and database servers.
  • Servers are usually located in data centers or centralized locations to ensure high availability and reliability.
Use Cases

  • Web Browsing: Web browsers (clients) request web pages and resources from web servers (servers) over the internet.
  • Email: Email clients (clients) retrieve, send, and manage emails stored on email servers (servers).
  • File Sharing: File transfer clients (clients) request files from file servers (servers) or peer-to-peer (P2P) networks.
  • Database Access: Database clients (clients) access data stored on database servers (servers) for various applications.
  • Cloud Computing: Cloud services often use the client-server model, with clients accessing resources and services hosted on cloud servers.
  • Online Gaming: Online gaming clients (players) connect to game servers (servers) to participate in multiplayer games.

  • I have “sshd” installed in my machine and I try to connect to a server using ssh command as follows:
$ ssh flexiadmin@10.241.9.XXX
flexiadmin@10.241.9.XXX's password:

  • My local machine has “sshd” client which is connected to “sshd” running on remote server with IP 10.241.9.XXX

  • Through “netstat” command on my local machine, we can see that client “sshd” is connected to server “sshd”

# netstat -apn | grep ssh
tcp 0 0 10.241.9.XXX:22 ESTABLISHED 14541/ssh

  • Here is my local IP and 10.241.9.XXX is the server IP.

  • It can also be seen from the above output that, on the server, “sshd” is listening on port 22 and on my local machine, “sshd” client used some random port (37026) to connect to the server on port 22.
Common issues with Client-Server model

Connectivity Problems:

Server Unavailability: If the server is down or experiencing issues, clients cannot connect or access services.
Network Interruptions: Network problems, such as slow or unreliable connections, can disrupt communication between clients and servers.

Latency and Delays:

Slow Response: High server load or network congestion can lead to slow response times, causing frustration for users.
Lag in Real-Time Applications: In real-time applications like online gaming or video conferencing, latency can result in delayed interactions or poor user experiences.

Data Loss or Corruption:

Packet Loss: Network packet loss can lead to data loss or corruption during transmission.
Server Failures: Data can be lost if the server crashes or experiences hardware failures.

Security Concerns:

Data Breaches: Inadequate security measures can lead to data breaches or unauthorized access to sensitive information.
Malware and Attacks: Clients or servers may become vulnerable to malware or hacking attempts.
Common Troubleshooting Techniques

Check Network Connectivity:
Verify client-server communication.
Test DNS resolution and network connectivity.

Review Server Logs:
Examine server logs for errors or warnings.

Check Client Logs:
Review client application logs for insights.

Verify Server Status:
Confirm the server is operational.
Check resource usage for constraints.

Monitor Network Traffic:
Use monitoring tools to analyze traffic.

Check Firewalls and Security Settings:
Ensure no blocking of necessary ports.
Review security configurations.

Inspect Application Code:
Review code for bugs or misconfigurations.

Review Server Configuration:
Check software and database configurations.

Check for Software Updates:
Ensure client and server software are up-to-date.

Load Balancing and Scaling:
Verify even traffic distribution.
Assess scalability for increased loads.

Isolate Components:
Test and isolate individual components to identify the cause.