Skip to content

Latest commit

 

History

History
executable file
·
128 lines (88 loc) · 5.05 KB

networkingLayer3NetworkIP.md

File metadata and controls

executable file
·
128 lines (88 loc) · 5.05 KB
Raw

Layer 3 - Network

  1. We want to transfer data from one IP address to another.
  2. First device emits a broadcast only the subnet can see, i.e. local network.
  3. IF device is not there, the data is forwarded to the router.
  4. Routers pass on the data until the matching subnet is reached.
  5. Data enters that network and goes to the desired IP address in that local network.

Public (WAN) vs Private (LAN)

You can't access the internet with a private (local) IP address.

The conversion from private (local) to public IP is done by NAT (Network Address Translation)

Public (WAN) Private/Local (LAN)
Unique Not unique, can be used on other private networks
Used externally Used internally
Assigned by ISP Assigned by the router's DHCP service

IP Address

A numeric identifier for a computer or device on a network.

It's composed of 4 octets in the 0-255 range.

[0-255].[0-255].[0-255].[0-255]

66.94.234.13

Computers read IP addresses in a binary format.

66.94.234.13 = 01000010.01011110.00011101.00001101
Octet Sum 128 64 32 16 8 4 2 1
66 64 + 2 0 1 0 0 0 0 1 0
94 64 + 16 + 8 + 4 + 2 0 1 0 1 1 1 1 0
234 16 + 8 + 4 + 1 0 0 0 1 1 1 0 1
13 8 + 4 + 1 0 0 0 0 1 1 0 1

Subnet

Used to break down larger networks into smaller ones (subnets).

IP addresses have 2 parts, and the subnet mask determines which part is the network and the host, by masking the bits used for the network.

# Network address
192.168.100.0

# Host addresses
192.168.100.1
192.168.100.2
192.168.100.3
IP address        192.168.1.0        11000000.10101000.00000001.00000000

Subnet Mask       255.255.255.0      11111111.11111111.11111111.00000000
                                     -------------------------- --------
                                                Network           Host

Subnet Mask       255.255.224.0      11111111.11111111.111 00000.00000000
                                     --------------------- --------------
                                              Network           Host

# CIDR Notation - Classless Inter-Domain Routing (slash notation)

192.168.1.0 /24   =   24 bit subnet mask

11111111.11111111.11111111.00000000   =   255.255.255.0
CIDR Subnet mask Binary Networks Hosts
/24 255.255.255.0 11111111.11111111.11111111.00000000 1 254
/25 255.255.255.128 11111111.11111111.11111111.10000000 2 126
/26 255.255.255.192 11111111.11111111.11111111.11000000 4 62
/27 255.255.255.224 11111111.11111111.11111111.11100000 8 30
/28 255.255.255.240 11111111.11111111.11111111.11110000 16 14
/29 255.255.255.248 11111111.11111111.11111111.11111000 32 6
/30 255.255.255.252 11111111.11111111.11111111.11111100 64 2
/31 255.255.255.254 11111111.11111111.11111111.11111110 128 0

Classes

User Class First octet address Default subnet mask Hosts
ISP A 1 - 126 255.0.0.0 16 M
Large organization A 128 - 191 255.255.0.0 65 K
Small organization / home A 192 - 223 255.255.255.0 254

DHCP - Dynamic Host Configuration Protocol

A service that runs on a router or server, which automatically assigns:

  • IP address
  • Subnet mask
  • Default gateway
  • DNS server

It leases the IP addresses to all devices connected to it. It leases them instead of giving to prevent running out of them ex. when a PC is removed, it would take the address with it.

The computers given the addresses ping the DHCP server on intervals to renew their lease, otherwise the address returns to the pool.

You can assign a static address via reservation. They are usually assigned to printers, routers, servers...

Before this service, you had to manually input all the parameters for each device in the network.

NAT - Network Address Translation

Private to public IP address conversion, and vice-versa.

Default Gateway (Router)

Majority of times it's a router.

Forwards data from one network to another.

Gateway is the router address we are talking to in order to connect to the rest of the network/internet.