Internet Protocol version 4 (IPv4) protocol notes

1. Advantages of IPv4 (Legacy Strengths)

  • Universality: Supported by every network device and application globally.

  • Simplicity: Mature and well-understood, with extensive troubleshooting tools.

  • NAT (Network Address Translation): Conserves public addresses and adds a layer of privacy.

  • Broadcast Support: Built-in mechanism for network-wide announcements.

2. Writing IPv4 Addresses (Best Practices)

  • Dotted-Decimal Notation: Four 8-bit octets separated by dots (e.g., 192.168.1.1).

  • CIDR Notation: Always include prefix length (subnet mask) (e.g., 192.168.1.0/24).

  • Private Address Ranges:

    • 10.0.0.0/8

    • 172.16.0.0/12

    • 192.168.0.0/16

  • Avoid Leading Zeros: Write 192.168.1.1, not 192.168.001.001.

3. IPv4 Address Types & Scopes

Type

Range

Scope

Use Case

Public

Except private ranges

Global (internet)

Routable on the internet.

Private

10.0.0.0/8

Site-local

Internal networks, NATed for internet.

172.16.0.0/12

192.168.0.0/16

APIPA

169.254.0.0/16

Link-local

Auto-configured when DHCP fails.

Loopback

127.0.0.0/8

Node-local

Localhost (typically 127.0.0.1).

Broadcast

Subnet-specific

Subnet-local

Send to all hosts on the subnet.

Multicast

224.0.0.0/4

Defined by TTL

Group communication (e.g., 224.0.0.9 for RIP).

4. Calculating IPv4 Subnets

  • Subnetting borrows bits from the host portion to create subnets.

  • Formula: Number of subnets = 2^(borrowed_bits)

  • Hosts per subnet = 2^(remaining_host_bits) - 2 (subtract network & broadcast).

  • Example: Subnet 192.168.1.0/24 into four /26 subnets:

    • Borrowed bits: 26 - 24 = 2 → 2^2 = 4 subnets.

    • Subnets: 192.168.1.0/26, .64/26, .128/26, .192/26.

    • Hosts per subnet: 2^(6) - 2 = 62.

  • ARP (Address Resolution Protocol): Maps IP addresses to MAC addresses.

  • DHCP (Dynamic Host Configuration): Assigns IP addresses and configs to hosts.

  • ICMP (Internet Control Message Protocol): Error reporting and diagnostics (e.g., ping).

  • NAT (Network Address Translation): Translates private IPs to public IPs.

  • DNS (Domain Name System): Resolves domain names to IP addresses.

6. Characteristics & Security Concerns

  • Characteristics:

    • Uses broadcast for network-wide communication.

    • Relies on NAT for address conservation.

    • Header includes checksum for error detection.

  • Security Concerns:

    • NAT Limitations: Breaks end-to-end connectivity, complicating applications like VoIP.

    • ARP Spoofing: Attackers poison ARP tables to intercept traffic.

    • Broadcast Storms: Misconfigurations can lead to network congestion.

    • Address Exhaustion: Limited address space (4.3 billion addresses) has been depleted.

    • Fragmentation Attacks: Maliciously crafted packets can evade security controls.

7. Creating an IPv4 Addressing Plan

  1. Determine Needs: Estimate the number of subnets and hosts per subnet.

  2. Choose Private Range: Select 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16.

  3. Subnet Efficiently:

    • Use VLSM (Variable Length Subnet Masking) to avoid waste.

    • Example: Use /30 for point-to-point links (2 hosts), /24 for user LANs.

  4. Reserve Addresses:

    • Reserve first/last addresses for network/broadcast.

    • Reserve blocks for infrastructure (e.g., routers, servers).

  5. Documentation: Maintain a subnetting table with assignments.

8. IPv4 Transition Mechanisms to IPv6

  • Dual Stack: Devices run both IPv4 and IPv6 simultaneously.

  • Tunneling: Encapsulate IPv6 in IPv4 packets (e.g., 6to4, Teredo).

  • Translation: Convert IPv4 to IPv6 (e.g., NAT64 with DNS64).

  • Proxying: Use a proxy to mediate between IPv4 and IPv6 hosts.

Quick Reference

  • /24: Common subnet mask for small networks (254 hosts).

  • /30: Typical for point-to-point links (2 hosts).

  • Private Ranges: Use 10.0.0.0/8 for large networks, 192.168.0.0/16 for homes.

  • NAT: Essential for connecting private networks to the internet.