DNS uses several common record types. Each record type has a unique function: A records - address recordsAAAA records - connects domain names to IPv6 addressesCNAME records - links subdomains to domain A or AAAA recordsMX records - directs emails to the domain mail serverNS records - shows which DNS server is acting as the authoritative nameserver for the domainTXT records - stores textual information related to domainsYou can create a DNS record by selecting a record type and filling in the required information for that record type

Domain Name System

Buttons to display information about DNS record types A AAAA CNAME MX NS TXT Information section for DNS record types Click on the buttons above to see the description of each DNS record type. Buttons to display information about domain types .com .net .org .gov Information section for domain types Click on the buttons above to see the description of each domain type. Form for DNS record creation Select Record Type: A (Address Record)AAAA (IPv6 Address Record)CNAME (Alias Record)MX (Mail Exchange Record)NS (Name Server Record)TXT (Text Record) Domain Name: IP Address: Alias (CNAME): MX Priority: TXT Value: Create Record Table to display created DNS records Record TypeDomainDetails DNS records will be dynamically added here

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Next

DNS Simulation

Use the dropdowns to select a user and a domain name. You can also enter a custom URL to simulate the function of the DNS server.

Internal DNS Server (192.168.1.100) Centered container for the page content DNS Resolution Table for Local Domains Domain NameIP Address WWW.LAN121.COM 192.168.1.101 FILES.LAN121.COM 192.168.1.102 EMAIL.LAN121.COM 192.168.1.103 Select a station (user) and a URL to simulate a DNS request. Control Panel Dropdown for selecting a station (user) User 1User 2User 3User 4User 5 Dropdown for selecting a predefined domain WWW.LAN121.COMFILES.LAN121.COMEMAIL.LAN121.COMGOOGLE.COMYOUTUBE.COM Input field for custom URL Button to send DNS request Send DNS Request Output log

Principles of Modern Communication

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Network Services

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DHCP

Select Workstation: Workstation 1Workstation 2Workstation 3 Discover Offer Request Acknowledge Reset Click on the buttons above to see each step of the DHCP process. DHCP Server Available Addresses IP Address 192.168.1.16 192.168.1.17 192.168.1.18 192.168.1.19 192.168.1.20 192.168.1.21 192.168.1.22 192.168.1.23 192.168.1.24 Workstation 1 Workstation 2 Workstation 3

Dynamic Host Configuration Protocol (DHCP) Port 67, 68

Hypertext Transfer Protocol (HTTP/HTTPS) Port 80, 443

Network services are critical functions that enable devices to communicate, share resources, and maintain efficient network operations. These services form the backbone of modern networks, facilitating connectivity and resource management. Each network service is associated with a port number. Port numbers ensure proper routing of data to the correct service.

Internet Control Message Protocol (ICMP) Uses types/codes

Introduction

Domain Name System (DNS) Port 53

Simple Mail Transfer Protocol (SMTP) Port 25

Network Time Protocol  (NTP) Port 123

File Transfer Protocol (FTP) Port 20, 21

Network Services

Menu

2) The root server is like an index in a library that points to different racks of books—it is the first step in resolving a host name and it typically serves as a reference to a more specific location.

Query

3) Top level domain server (TLD) searches for a specific IP address, and it hosts the last portion of a hostname (think of the TLD as the specific rack of books in the library.

Recursor Server

Domain Name System (DNS)

4) The authoritative name server is the last stop in the nameserver query—if it has access to the requested record, it returns the IP address for the requested hostname back to the DNS Recursor (the librarian).

Click here

Client

1) The DNS recursor receives queries from client machines using web browsers. The recursor is like the librarian who is asked to go find a particular book somewhere in the library.

DNS resolves (translates) human readable domain names like www.example.com into its machine readable IP address (192.168.1.1) to enable user-friendly web navigation. There are four DNS servers involved in loading a web page.

DHCP automates the assignment of IP addresses and other communication parameters to client devices. Network devices request an IP address and other network configuration information (subnet mask, default gateway, DNS server, lease duration, and NTP server among others). The DHCP Request and Response Process DORA/ROSA:Discovery: Client requests an IP address.Offer: Server offers an available IP.Request: Client accepts the offer.Acknowledgment: Server confirms the assignment.The benefit of DHCP is that it reduces manual IP configuration and prevents IP conflicts.

Dynamic Host Control Protocol (DHCP)

Network Address: Subnet Mask: Default Gateway: DNS Server: Starting Host Address: Number of Addresses to Assign: Lease Time (hours): Create Pool Configured DHCP Pools Network AddressSubnet MaskDefault GatewayDNS ServerStarting Host AddressNumber of AddressesLease Time (hours)

Click to send packet

Link Failure

Internet Control Message Protocol (ICMP)

Source Device

Destination  is unreachable

Destination Device

ICMP helps to maintain and troubleshoot network health by sending error messages back to the source device when a packet cannot be delivered informing about issues like unreachable hosts, network errors, or time exceeded limits. ICMP messages contain a field that indicates the type of error and a code field for further details about a specific issue.

Client

File Transfer Protocol (FTP)

Control Connection

FTP operates on a client-server architecture—a user is the client requesting files from a remote server that stores the data. FTP opens two connections that link the computers trying to communicate with each other.

Server

User logs in to the FTP server

FTP uses two connections to allow commands and file data flow

Data Connection

The user can perform upload, download, delete, and rename files on the remote server using commands through the control connection

Username Pass****

The mail server receives the email and stores it in the mailbox so that she can read it later

Send Email

ABC Corp SMTP Server

XYZ Corp SMTP Server

Simple Mail Transfer Protocol

The SMTP server receives the email sent by a client and routes it to the recipient’s mail server. The recipient’s email server stores the email until the recipient retrieves it using protocols such as IMAP or POP3.

Server sends the requested web page

Hypertext Transfer Protocol (HTTP)

HTTP facilitates the transfer of web pages and resources between browsers and servers. HTTPS secures this communication using encryption. 

Browser requests a  web page

7:50:45

The central “timekeeper” (like an atomic clock) distributes the most accurate time through the network of servers ensuring all clocks are synchronized and showing the same time.

Each level further down the tree structure represents a “stratum” of servers progressively further away from the original source. Each device on the network pulls time from a nearby server in the hierarchy.

Stratum 1

Stratum 2

7:50:59

Network Time Protocol (NTP)

Stratum 3

7:49:45

7:51:00

7:50:07

NTP synchronizes the clocks of devices across a network. Devices query NTP servers for accurate timestamps. This ensures accurate time for logging, security events, and scheduled tasks.

7:51:01

7:49:49

7:50:10

7:50:33

7:50:19

7:50:20

7:49:04

7:50:30

Clocks Synchronized