Networking

Basic Networking Terms:-

LAN -> Local Area Network

• Collection of devices connected together in one physical location.
• Each device has a unique IP(Internet Protocol) address.
• Devices communicate via these IP addresses.

IP -> Internet Protocol

• 32-bit value.
• 1 bit : 1 or 0.
• 00000000 : 0
• 11111111 : 255

Eg; 172.16.0.0

• IP addresses can range from 0.0.0.0 to 255.255.255.255

Switch

• Sits within the LAN.
• Facilitates the connection between all the devices within the LAN

Gateway -> IP address of Router.

Router

• Sits between LAN & outside networks (WAN: Wide Area Network).
• Connects devices on LAN & WAN.
• Allows networked devices to access the Internet.

Subnet -> Logical subdivision of an IP network.

How to know whether the other device is inside or outside the LAN?

• It knows because of the IP address of the target device.
• Devices in the LAN belong to the same IP address range.

Subnetting -> Process of dividing a network into two or more networks.

IP address range

CIDR*(Classless Inter-Domain Routing)* Block

• Subnet Mask dictates how many bits are fixed.
• 255.255.0.0 -> means that 16 bits are fixed
• 255.255.255.0 -> means that 24 bits are fixed

Any device needs 3 pieces of data for communication:

• IP address
• Subnet
• Gateway

NAT*(Network Address Translation):*

• The IP address range is chosen by an administrator.
• Each device gets a unique IP from that range.

How to make sure that IP addresses don't overlap?

• IP addresses within LAN are not visible to the outside network or internet.
• Your laptop's private IP address is replaced by the router.

Benefits of NAT;

• Security & Protection of devices within LAN.
• Reuse IP addresses.

Limited no. of IPv4 addresses available - 4,294,967,296 public addresses.

Firewall

• A system that prevents unauthorized access from entering a private network.
• Using Firewall Rules you can define, which requests are allowed.

Firewall Rules;

• Which IP address in your network is accessible
• Which IP address can access your server.
• You can, e.g., allow any device to access your server.
• Allows device IP address at the port to be accessed.
• This is also called Port Forwarding

What is a Port?

Port -> every device has a set of ports.

• You can allow specific ports(doors).
• You can allow specific ports(doors) AND specific IP addresses (guests).
• Different Applications listen to specific ports.

Standard Ports for many applications:-

• Port 80 -> Web Servers
• Port 3306 -> MySQL DB
• Port 5432 -> PostgresQL DB

For every application, you need a port!

Each port is unique on a device.

DNS -> Domain Name Service

• Translates domain names to IP addresses.

Why do we use names instead of IP addresses?

• Humans are better at remembering words & names instead of numbers.

Eg; www.facebook.com -> 69.63.176.13 Mapping IP addresses to Names.

How does DNS manage all these IP addresses?

• Domain Names have a hierarchical structure.

Root Domains (there are 13 root domains named from a to m)

Top Level Domain

There are also geographical domains that were added later.

Who manages these names?

Who can keeps track of the availability of names?

This is all regulated by a dedicated organization called Internet Corporation for Assigned Names & Numbers (ICANN).

• Manages the TLD development and architecture of the internet domain space.
• Authorizes Domain Name Registrars, which register & assign domain names.

Each domain name can have a subdomain name with IP address range of domain name

How does the DNS Resolution work?

DNS entries are cached for efficiency

Networking Commands:

• ifconfig -> shows all network details.
• netstat -> shows active connection on your machine.
• ps -aux -> shows currently running applications on which port they are listening, computer resources they are consuming, etc.
• nslookup -> you can get the IP address of any domain name.
• ping -> checks whether a service/application is accessible.

These are used to

• Troubleshoot your network
• Of course, there are parameters for all those commands.