Module 2 cheat sheet: Networking Foundations

IP addresses find devices, ports find services, and CIDR blocks size the networks you will build as VPCs.

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Key ideas

  • PAN < LAN < CAN < MAN < WAN. Switch = inside a LAN (MAC); router = between networks (IP). Day 5 →
  • IPv4 = 32 bits, 4 octets of 0–255. Bits: 128 64 32 16 8 4 2 1. Day 6 →
  • First address = network ID, last = broadcast: never for devices. Day 6 →
  • Private ranges: 10/8, 172.16/12, 192.168/16; NAT shares one public IP. Day 7 →
  • DHCP gives IPs automatically: DORA. Day 7 →

Ports to remember

PortService
22SSH (Linux login)
80HTTP
443HTTPS
3389RDP (Windows login)
3306MySQL

CIDR quick table

addresses = 2^(32 − prefix) · usable = − 2 · in AWS = − 5
CIDRAddressesAWS usable
/1665,53665,531
/204,0964,091
/24256251
/281611
/321 (one IP)n/a

Classes

ClassFirst octetDefault mask
A1–126/8
B128–191/16
C192–223/24
D224–239multicast
E240–255research

Special addresses

AddressMeaning
0.0.0.0/0anywhere (in AWS rules)
127.0.0.1loopback
169.254.x.xAPIPA (no DHCP)
169.254.169.254EC2 instance metadata

Common mistakes

  • Overlapping VPC CIDRs that can never be connected later.
  • Forgetting AWS reserves 5 IPs per subnet.
  • Opening SSH/RDP to 0.0.0.0/0.
  • Thinking IP itself uses ports (TCP/UDP do).

Created by Ajeetkumar · EasyLearnSpace