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IP Fundamental

Table of contents

IP - layer 3

  • IPv4 uses 32-bit addresses
4 x 8 bits = 32 (4 x octet, 1 octet = 8 bits)
aaaaaaaa bbbbbbbb cccccccc dddddddd -> xxx.xxx.xxx.xxx
  • Run ifconfig
inet -> ipv4 
inet6 -> ipv6

Binary to Decimal 

  1    1    1    1   1   1   1   1 = 183
128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 183
-----> * count start right (small number) to left (large number) 
  1   0    1    1   0   1   1   1 = 183
128 + 0 + 32 + 16 + 0 + 4 + 2 + 1 = 183
  • ipv4 availability = 2 ^ 32 = 4,294,967,296 (4 billion)
  • ipv6 availability = 2 ^ 128 = xxxxxx

Private IP address

Private-IP-Table

CIDR notation - subnetting

  • CIDR: Classless Inter-Domain Routing
  • Understand Mbps (megabits for speed) vs MBps (megabytes for data)
  • Most common: 255.255.255.0 = /24, 256 hosts available for this.
Example IP: 192.168.2.64/26
`/26` is subnet mask
/26 -> 26 x 1 -> 11111111   11111111   1111111   11 000000 (subnet mask)
                 --------   --------   --------  -- ------

                    192        168        2          64
                 11000000   10101000   00000010  01 000000 (ip address)  
                 --------   --------   --------  -- ------
                   fixed      fixed      fixed    | 000000 (lowest) -> network address 
                                                  | any number in between -> host ID
                   fixed      fixed      fixed    | 111111 (highest) -> broadcast address  

conclusion: 
11000000   10101000   00000010  01000000 -> 192.168.2.64 -> network ID
11000000   10101000   00000010  01111111 -> 192.168.2.127 -> broadcast ID 
192.168.2.64 -> xxx.xxx.x.65 ... -> 126 are the host ID

------------------------------------------------------------------------------
|    subnet   |  1   |  2   |  4   |  8   |  16  |  32  |  64  |  128 |  256 | pervious x 2
|     host    |  256 |  128 |  64  |  32  |  16  |  8   |  4   |  2   |  1   | pervious / 2
| subnet mask | /24  |  /25 |  /26 |  /27 |  /28 |  /29 |  /30 |  /31 |  /32 |
------------------------------------------------------------------------------

    Network                Host 
-----------------------------------
|  192  .  168  .  32  | .  152   |
|  255  .  255  . 255  | .   0    |
-----------------------------------
Class   Subnet Total available hosts
A 1.0.0.0 - 126.255.255.255 255.0.0.0 16,777,214
B 128.0.0.0 - 191.255.255.255 255.255.0.0 65,534
C 192.0.0.0 - 223.255.255.255 255.255.255.0 254
D & E E is reserved    
  • Public ip: unique, one ip per household
  • Private ip: reusable range from 192.168.0.1 to 192.168.0.255, for printer, phone, ip per device.

MAC address (layer 2, relating to switch) 

ether = mac address: 82:bf:72:63:40:05 (use mac address lookup, virgin media)
                     --------
                     first 3 pairs is `identifier`

TCP, UDP, and the 3-way handshake (layer 4)

  • SYN > SYN ACK > ACK
  • 65,000 + ports available

Common ports and protocols:

TCP UDP
ftp 21 dns 53
ssh 22 dhcp 67, 68
telnet 23 tftp 69
smtp 25 snmp 161
dns 53  
pop3 110  
smb 139 + 445  
imap 143  

OSI model

Layers - Please Do Not Throw Sausage Pizza Away

  1. Physical - data cables, cat 6 - please
  2. Data - switching, MAC addresses - do
  3. Network - IP addresses, routing - not
  4. Transport - TCP / UDP - throw
  5. Session - session management - sausage
  6. Presentation - WMV, JPEG, MOV - pizza
  7. Application - HTTP, SMTP - away
Layer TCP / IP Model OSI model (7 layers)
L7 Application layer Presentation layer
  Session layer  
L4 Transport layer Transport layer / UDP header / tcp header
L3 Internet Layer network layer / ip protocol layer / IP header
L2 network access layer Data Link Layer
  physical layer