Code-Memo

IP addressing and subnetting

IPv4 basics

IPv4 address: 32-bit, written as a.b.c.d
Subnet mask/prefix: /24 means 24 network bits, 8 host bits

CIDR quick examples

/24 → 256 addresses (254 usable in classic subnetting)
/25 → 128 addresses
/26 → 64 addresses
/30 → 4 addresses (often for point-to-point)

Calculate network info (quick mental model)

Identify the prefix length (e.g. /26)
Block size in the changing octet: (256 - \text{maskOctet})
Network boundaries occur at multiples of block size

View IP config on Linux

ip addr
ip route
ip -br addr
ip -br route

Private ranges

10.0.0.0/8
172.16.0.0/12
192.168.0.0/16

IPv6 notes (very short)

128-bit, hex groups, :: compression
Common prefix: /64 for LAN