Ipv4

Every node in an ipv4 network is assigned a 32bit address, unique to that network.
Networks can be divided into subnets. Two nodes that have been assigned ip-addresses
on 2x different subnets of the same network cannot communicate directly with each other.
They much first pass through a router.

Documentation

microsoft subnet docs

https://support.microsoft.com/en-us/help/164015/understanding-tcp-ip-addressing-and-subnetting-basics

IP addresses

IP Addresses are made up of 4x binary numbers in the range of (0-255) (32x bits). They are divided into a prefix, and the remaining of the 32bits form the address itself.

  192.168.1.100/24
= 11000000.10101000.00000001.1100100  # with 24bit prefix
  |                        | |     |
  +------------------------+ +-----+
      (24bits of  netmask)  (8bits of addr)


  192.168.1.100/16
= 11000000.10101000.00000001.1100100  # with 16bit prefix
  |               | |              |
  +---------------+ +--------------+
  (16bits of  netmask) (16bits of addr)

Reserved IP Address Ranges

127.0.0.1                     # loopback address
224.0.0.0 - 239.255.255.255   # reserved for multicast (address bound to group of addresses)

Non-Routable IP Address Ranges

These are routable within interior gateway protocols, but not exterior gateway protocols.

10.0.0.0/8
172.16.0.0/12
192.168.0.0/16

Subnets

CIDR and decimal notation

Subnets are bitmasks. The 1s in the address determine which parts of the address
identify the network, and the remainder identifies the recipient.

The first and last address on each subnet are reserved.

• the first is the network address
• the last is the broadcast address

There are 3x notations for netmasks:

192.168.1.1/24     # CIDR notation
255.255.255.0      # bitmask/netmask
class A            # (deprecated) class A/B/C IP addresses

# CIDR      netmask         # binary                             num_addrs  num_hosts  
  /31    255.255.255.254    11111111.11111111.11111111.11111110                        
  /30    255.255.255.252    11111111.11111111.11111111.11111100    4          2        
  /29    255.255.255.248    11111111.11111111.11111111.11111000    8          6        
  /28    255.255.255.240    11111111.11111111.11111111.11110000    16         14       
  /27    255.255.255.224    11111111.11111111.11111111.11100000    32         30       
  /26    255.255.255.192    11111111.11111111.11111111.11000000    64         62       
  /25    255.255.255.128    11111111.11111111.11111111.10000000    128        126      
  /24    255.255.255.0      11111111.11111111.11111111.00000000    256        254      
  /23    255.255.254.0      11111111.11111111.11111110.00000000    512        510      
  /22    255.255.252.0      11111111.11111111.11111100.00000000    1024       1022     
  /21    255.255.248.0      11111111.11111111.11111000.00000000    2048       2046     
  /20    255.255.240.0      11111111.11111111.11110000.00000000    4096       4094     
  /19    255.255.224.0      11111111.11111111.11100000.00000000    8192       8190     
  /18    255.255.192.0      11111111.11111111.11000000.00000000    16384      16382    
  /17    255.255.128.0      11111111.11111111.10000000.00000000    32768      32766    
  /16    255.255.0.0        11111111.11111111.00000000.00000000    65536      65534

IP class A, B, C

Before subnets existed, there were 3 classes of IP ranges
class A, B, and C.