Set 8 — IP Addressing and Subnetting Basics

IPv4 address length

32-bit, written as 4 octets (e.g. 192.168.1.4)

IPv4 octet range

0-255 per octet

Subnet mask

Defines which part of an IP is the network portion vs host portion

Class A default mask

255.0.0.0 (/8)

Class B default mask

255.255.0.0 (/16)

Class C default mask

255.255.255.0 (/24)

CIDR notation

Shorthand like /24 showing how many bits are the network portion

Classful vs Classless

Classful = fixed A/B/C masks; Classless (CIDR) = flexible mask sizes

Private range - 10.x

10.0.0.0 - 10.255.255.255 (/8)

Private range - 172.16.x

172.16.0.0 - 172.31.255.255 (/12)

Private range - 192.168.x

192.168.0.0 - 192.168.255.255 (/16)

APIPA range

169.254.0.0 - 169.254.255.255 (self-assigned when DHCP fails)

Loopback address

127.0.0.1 (tests the local device's own network stack)

Network address

The FIRST address in a subnet - identifies the network itself

Broadcast address

The LAST address in a subnet - sends to every device on it

NAT

Lets multiple private devices share one public IP address

Public IP

Globally unique, routable on the internet

Private IP

Only unique within the LAN, not routable on the internet

Static IP

Manually/permanently assigned address

Dynamic IP

Automatically assigned by DHCP, can change

IPv6 address length

128-bit

IPv6 format

8 groups of 4 hex digits separated by colons

IPv6 shorthand rule - leading zeros

Leading zeros in a group can be dropped

IPv6 shorthand rule - double colon

One run of all-zero groups can be replaced with :: (only once per address)

IPv6 loopback

::1

IPv6 link-local

fe80::/10 - auto-assigned, not routable off the local segment

IPv6 unique local

fc00::/7 - IPv6's version of a private address

IPv6 global unicast

Publicly routable IPv6 address (like a public IPv4 address)

IPv4's biggest limitation

Only ~4.3 billion addresses (32-bit space) - solved by NAT + private IPs