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IP Addresses

Definition

An Internet Protocol (IP) address is a unique numerical identifier assigned to every device participating in a computer network that uses the Internet Protocol for communication. It serves two primary functions:

  • Identification: Uniquely identifies a device on the network
  • Location Addressing: Provides the means to route packets of data to and from devices across interconnected networks

An IP address operates within the framework of the Internet Protocol, which is a set of rules governing the format of data sent via the internet or local networks.

Structure and Types of IP Addresses

IPv4 (Internet Protocol Version 4)

  • IPv4 addresses are 32-bit numbers, represented in dotted-decimal notation (e.g., 192.168.1.1)
  • Composed of four octets (8-bit segments), each ranging from 0 to 255
  • IPv4 supports approximately 4.3 billion unique addresses (2³²), leading to address exhaustion

IPv6 (Internet Protocol Version 6)

  • IPv6 addresses are 128-bit numbers, represented in colon-separated hexadecimal notation (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334)
  • Provides a vastly larger address space of 2¹²⁸ possible addresses
  • IPv6 includes built-in features such as:
    • Improved security (IPsec)
    • Auto-configuration
    • Better routing efficiency

How IP Addresses Work

The operation of IP addresses occurs at the Network Layer (Layer 3) in the OSI model. Below is an in-depth explanation of their functionality.

Address Assignment

  • Static IP: Manually assigned by an administrator and remains constant
  • Dynamic IP: Automatically assigned by a Dynamic Host Configuration Protocol (DHCP) server, used for flexibility in consumer networks
  • Private vs. Public IPs:
    • Private IPs: Reserved for internal networks (e.g., 192.168.x.x, 10.x.x.x), not routable on the internet
    • Public IPs: Globally unique and routable on the internet, assigned by an Internet Service Provider (ISP)

IP Address Components

  • Network Identifier (NetID):
    • Specifies the network to which the device belongs
    • Determined by the subnet mask (e.g., /24 in CIDR notation)
  • Host Identifier (HostID):
    • Identifies a specific device within the network
    • The size of the HostID is inversely proportional to the NetID

Routing and Communication

IP addresses enable data transfer by serving as endpoints in a packet-switching network. Key processes include:

  • Address Resolution:
    • Devices translate domain names into IP addresses using the Domain Name System (DNS)
    • ARP (Address Resolution Protocol) maps IP addresses to MAC (Media Access Control) addresses within local networks
  • Packet Routing:
    • Data is divided into packets, each containing a source and destination IP
    • Routers use routing tables to determine the optimal path for packets
    • Packets traverse multiple routers to reach the target destination
  • Encapsulation and Decapsulation:
    • Data at the sender's end is encapsulated with headers (including IP address) and transmitted
    • At the receiver's end, headers are stripped to extract the data

IP Classes and Subnetting

Classful IP Addressing

Historically, IPv4 addresses were divided into classes (A, B, C, D, E) based on the range of the first octet.

Subnetting

Subnet masks (e.g., 255.255.255.0) divide IP addresses into smaller, manageable sub-networks, improving address utilization and network performance.

IP Protocols and Mechanisms

Connectionless and Best-Effort Delivery

  • The Internet Protocol is connectionless, meaning it does not establish a dedicated path before transmitting data
  • It uses a best-effort delivery model without guarantees for delivery, order, or error correction. These functions are handled by higher-layer protocols like TCP

Fragmentation and Reassembly

  • If a packet exceeds the Maximum Transmission Unit (MTU) of a network segment, it is fragmented into smaller packets
  • The receiving device reassembles these fragments using identification and offset information in the IP header

Challenges and Modern Solutions

IPv4 Address Exhaustion

The growth of devices has depleted IPv4 addresses. Solutions include:

  • Network Address Translation (NAT): Allows multiple devices to share a single public IP
  • IPv6 Adoption: Offers a nearly limitless pool of addresses

Security

IP addresses are vulnerable to spoofing, denial-of-service (DoS) attacks, and other exploits. Modern networks implement:

  • Firewalls
  • IPsec
  • VPNs

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