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Module 4: Network Layer

The Network Layer (Layer 3) is responsible for routing packets across different networks. The primary protocol is Internet Protocol (IP).
IP Routing Fundamentals

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4.1 IP Addressing (IPv4)

An IPv4 address is a 32-bit number, typically written in dotted-decimal notation (e.g., 192.168.1.1).

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Classes (Legacy)

  • Class A: 0.0.0.0 - 127.255.255.255 (Large networks)
  • Class B: 128.0.0.0 - 191.255.255.255 (Medium networks)
  • Class C: 192.0.0.0 - 223.255.255.255 (Small networks)

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Private IP Addresses (RFC 1918)

  • 10.0.0.0/8
  • 172.16.0.0/12
  • 192.168.0.0/16

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4.2 Subnetting

Subnetting divides a network into smaller, manageable sub-networks.
  • Subnet Mask: Determines which part of the IP is the Network ID and which is the Host ID.
  • Example: 255.255.255.0 (/24) means first 24 bits are Network ID.

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4.3 Routing

Routers operate at Layer 3. They connect different networks and decide the best path for packets.

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Routing Protocols

  • IGP (Interior Gateway Protocol): Used within an autonomous system (e.g., OSPF, RIP).
  • EGP (Exterior Gateway Protocol): Used between autonomous systems (e.g., BGP).

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Next Module

Module 5: Transport Layer

TCP vs UDP and reliability.