Application Layer

Protocols

Manual Configuration and DHCP

DHCP (Dynamic Host Configuration Protocol) automates the assignment of IP addresses, subnet masks, default gateways, and DNS settings to devices on a network. It allows devices to receive network configurations automatically, eliminating the need for manual setup, which simplifies management and reduces configuration errors.

In manual DHCP configuration, the administrator specifies certain network parameters to assign fixed IP addresses to devices, which is particularly useful for servers and other critical devices that require a static IP.

TOPOLOGY

Routers CLI

Configuring left sub part of network

Configuring right sub part of network

IP address assigned to PC0 through DHCP

DNS,SMTP,HTTP DEMONSTRATION

Topology

DNS

DNS functions like the "phonebook" of the internet, translating user-friendly domain names (e.g., www.example.com) into IP addresses (e.g., 192.0.2.1) that computers use to identify and locate each other on the network.

When a user enters a domain name in a browser, a DNS query is sent to the DNS server to retrieve the corresponding IP address. This query may involve multiple DNS servers in a hierarchical structure, including root servers, top-level domain (TLD) servers, and authoritative DNS servers, working together to find the correct IP address.

DNS hierarchy

Adding records to DNS server

DNS query resolution

SMTP

SMTP is responsible for sending and routing emails across networks, facilitating the transfer of messages from a mail client (such as an email application) to a mail server and between mail servers for further delivery. When an email is sent, the client connects to an SMTP server and transfers the message along with the recipient’s details. The SMTP server identifies the recipient’s domain and forwards the message either to the recipient’s server or directly to their mailbox if it's on the same server. This process can involve multiple SMTP servers relaying the message to ensure it reaches its final destination.

SMTP server setup

Mail Sent

Mail Recived

HTTP

HTTP is the protocol responsible for transferring web pages and resources, like images and scripts, across the internet, forming the foundation of data communication on the World Wide Web. When a user requests a webpage by entering a URL into a browser, the browser sends an HTTP GET request to the server hosting the page. The server then responds with the HTML content, which the browser renders as a visual webpage. HTTP is a stateless protocol, meaning each request operates independently of others; however, modern implementations often use cookies to maintain session state across requests.

HTTP server setup

HTTP request

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