IT and security stuff

Domain, DHCP and DNS

Definition of a domain:

  • Computer network
  • User accounts, computers, resources and security defined by a domain controller
  • Users and computers are authenticated on the domain controllers
  • The resources authorizations are based on “users and groups”

Short definition of a DNS server (Domain Name System)

  • Service which the main function is to translate a domain name into an IP address

Short Definition of a DHCP server (Dynamic Host Configuration Protocol):

  • Service that delivers the IP addresses to the connected machines
  • DNS and DHCP both work on the client-server structure but are different terms. DNS maps the domain name to the IP address while the DHCP is a protocol which assigns the IP address to the hosts in a network. Static or Dynamic

Domain Controller definition:

  • A Domain Controller is a server that responds to the authentication requests and controls the users into the network
  • The Domain Controller contains the data that validates the network access as well as the groups and computers names policies

Network structure:

Client-Client:

  • Every account are on each local computer. This makes security hard to manage and is not as robust as a true Domain
  • The files are stored on local machines or on a storage device connected to the network. Expect data loss
  • Printer and other devices are local and must be added and configured individually

Client-Server:

  • Centralized security. Passwords, authorization policies and other security functions are managed and an administrator on the Domain
  • The files can be stored on this machine
  • Backups are easier to manage
  • Centralized applications. Any apps used by a business can be installed or managed by a Domain Controller
  • Group strategies
  • Easier to manage and update
  • Server hardware is designed to for a continuous use

DNS

Definition:

DNS is for Domain Name Service/System. It is a protocol which allows to associate a name with an IP address.

A client(ex: web browser), sends a request to learn the IP address of the corresponding web server you reach.

Example: If you go on www.example.com, your browser must ask what is the IP address of the sub-domain “www” on the DNS Zone of example.com

Just like the DHCP Manager there is an DNS Manager. This console is dedicated to the DNS administration role allow to create the different zones to make DNS functionnal.

A direct zone allows the association of a name to an IP address, making it way simpler for us, humans, to remember than an IP address, which may change at any time.

Now that you have a direct zone, wouldn’t it be practical to create a reverse zone? Associating an IP address to a name. This allows to make sure the chosen name is associated with the intended IP address.

IIS(Internet Information Services) is the web server in Windows Server 2019. A web server is programmed in the client-server model, the world wide web(www) and Hypertext Transfert Protocol(http).

Dns records:

The A records link a domain name to the physical IP address of a computer hosting this domain.

example:

  • Add a new host(Name=PC1, IP Address=192.168.1.101)
  • Add a new host(Name=PC2, IP Address=192.168.1.102)
  • Add a new host(Name=PC3, IP Address=192.168.1.103).

The nslookup command can confirm this.

DHCP

Definition:

A DHCP server is a server or a service that delivers the IP addresses to the clients connecting on the network.

DHCP stands for Dynamic Host Configuration Protocol.

The NICs must be configured to receive automatically an address when it boots or joins the network. This is the case by default because it’s the easiest way to obtain an IP address.

It’s important to remember that an IP address must be unique on a network so the DHCP will manage this and will assign only new addresses to the new computer joining the network.

In fact, the DHCP server will deliver a lease with the IP. There are 3 interesting things in this lease:

  • Life term
  • Dynamic IP address
  • Network configurations

DHCP lease term:

The DHCP server has given us an IP address but it is limited in time(4h, 6h.. depends on the network configurations)

The leases are limited in time. Once it expires, the IP addresses become available once again.

  • If the computer is still connected, it will receive a new lease
  • If the computer is not connected, the IP address becomes available for another computer

Dynamic IP Address:

A Dynamic IP Adress means that it will changed every sessions.

An IP Adress by itself is not enough. It must be delivered with a subnet mask.

Finally, there are many advantages using DHCP:

  • No need to assign an IP address to a computer. It’s done by itself
  • The addresses management is completely automatic
  • The administration is centralized
  • The DHCP server/service will send other information about your network such as the router’s address or the DNS server

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