IT and security stuff

Networking basic concepts(WIP)

Why do we need a network ?

  • Share resources
  • Communicate: emails, chat, voIP
  • Control and monitor for security
  • Entertainment: video games, social media, etc.

Physical elements of a network

Hosts or “end devices”:

  • Clients
  • Servers(DNS, DHCP, NAT)
  • Devices(printer, phones, etc.)
  • External storage: NAS, SAN, etc.

Interconnection equipment:

  • Router, switch, etc.
  • Transmission media: network cables, optic fibber, radios

Local Area Network (LAN)

Often used by a small or medium business(business network or home network). Links computer, server and devices, usually in the same building. Shares common resources: files, folders, media, etc.

Metropolitan Network MAN

Usually Intermediate sized network. Can be used in large cities, to connect multiple cities or towns or a large area with several buildings. A MAN is larger than a LAN but smaller than a WAN.

Wide Area Network WAN

A very large network, like the internet(Inter Networking), the most popular WAN. A network of networks that allows communication with one another.

Client/Server?

Client:

  • The client is the one asking for “service”
  • The client sends a request to the server
  • The client requests are directed to network ports: FTP(21), HTTP(80), HTTPS(443)

Server:

  • The server is the one distributing the services.
  • The server is listening for incoming requests
  • The services can be a website, access to files and folders, etc.
  • The server listens on ports

What is a Windows Domain?

  • A sort of kingdom which is managed by the king(domain controller)
  • Allows to centralize the users, computer accounts with the help of an contact list service such as Active Directory.
  • Allows to control privileges for the domain users.

Virtualisation

  • A network can also rely on virtualisation servers
  • A physical service can host many virtual machines
  • There are many known hypervisors such as Microsoft Hyper-V, VMware, VirtualBox, etc

Advantages :

  • Allow the use of full potential on physical resources; RAM,CPU, etc.
  • A lot of power and resources saving
  • Allow the attribution several dedicated servers to a single task
  • Allows to implement secondary servers

Disadvantages:

  • A virtual server is not a powerful as a physical server
  • If the host or the virtualisation server fails, the who network fails
  • Certain specific related problems to the virtualisation itself

to be continued next class….

Network Interface Card (NIC)

  • The NIC allows communication between a computer and the transmission equipment(cable, wifi, etc)
  • Every host needs a NIC to communicate
  • The NIC allows to send and receive
  • Can be integrated within the motherboard or added via PCI express ports

NIC : physical address vs logical address

A NIC needs 2 addresses to communicate:

Physical Address:

  • MAC Address (Media Access Control), is unique for every single device. Ex : 7Y-D5-2G-93-7H-76
  • This address is given by the manufacturer, usually not editable
  • Used for local communication

Logical Address:

  • The IPv4 or IPv6 which can be configured on the NIC. Easy to change. Ex: 172.16.0.50
  • Allows to move from a network to another, change network or for internet browsing.
  • Can be dynamic or static

For the network to function properly a NIC need the following configs:

  • IP address
  • Subnet Mask
  • Default Gateway address
  • At least one DNS address

NIC: static or dynamic?

  • By default, a NIC is set to dynamic
  • The computer which the NIC is set to dynamic will receive it’s IP from the DHCP server(Dynamic Host Configuration Protocol)
  • The server distributes the IP to it’s client from it’s “pool”
  • This address will change by itself
  • If no DHCP available, the computer will take a random address starting with 169.254.X.X
  • We can give a static configuration ourself. This config will never change as long as we don’t edit it

Transmission speed(negotiation)

A NIC can support many transmission speeds:

  • 10 Mbps(Ethernet or 10BASE-T)
  • 100mpbs(Fast Ethernet or 100BASE-T)
  • 1gbps(Gigabit Ethernet or 1000BASE-T)
  • 10gbps(10 gigabits Ethernet or 10GBASE-T)

Two modes

Full-Duplex:

  • Can send and receive at the same time.
  • A cable connection is usually Full-Duplex

Half-Duplex:

  • The NIC can only send or only receive.
  • Wifi is usually Half-Duplex

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