Networking Chapter 3: Addressing and Internet Structure

Chapter Three: Network Layer Addressing

• Network layer addressing is a critical component of network communication.
• The Internet is a network of networks.
• Until the early 1990s, the Internet was primarily used by academics, government, and industrial researchers.
• The World Wide Web (WWW) significantly expanded the Internet's user base in the 1990s.
• The Internet employs TCP/IP protocols and packet switching.

How the Internet Works

• Major backbone operators (like AT&T and Sprint) maintain large international networks.
• These networks are connected by high-bandwidth fiber optics and use thousands of routers.
• Large corporations and hosting services directly connect to these backbone networks.
• Network Access Points (NAPs) are locations where major backbones connect to enable packet switching between different backbones.
• A NAP typically consists of a Local Area Network (LAN) connecting all the routers of each backbone.
• The two central protocols are Transmission Control Protocol (TCP) and Internet Protocol (IP).

IP Versions and Addressing

• Each TCP/IP host is identified by a unique logical IP address.
• Every network component using TCP/IP needs a unique IP address.
• Each IP address includes a network ID and a host ID.
• Two IP versions exist: IPv4 and IPv6.
• IPv4 addresses use 32 bits, while IPv6 addresses use 128 bits.

IPv4

• IPv4 addresses consist of 32 bits of information.
• These bits are grouped into four sections, called octets or bytes.
• IP addresses can be represented in dotted-decimal, binary, or hexadecimal formats (e.g., 172.16.30.56).

Classifying IP Addresses

• There are five IP address classes: A, B, C, D, and E.
• Classes A, B, and C have different formats for splitting network ID and host ID.
• Class D is for multicast addresses.
• Class E is an experimental class and not widely used.
• The first four bits of an IP address determine its class.

Class A Addresses

• The first octet represents the network ID, the following three octets represent the host ID.
• There are limited Class A networks (126) that can accommodate a large number of hosts (>16 million per network).

Class B Addresses

• The first two octets mark the network ID, and the last two indicate the host ID.
• There are 16,384 networks available.
• Each network can support more than 65,000 hosts.

Class C Addresses

• The first three octets comprise the network ID, with the last octet representing the host ID.
• There are thousands of networks available and they can support 254 hosts.

Subnets and Subnet Masks

• Subnetting allows for smaller logical networks and more efficient use of IP addresses compared to fixed class-based networks.
• It improves network performance by limiting broadcast domains.
• Subnets can be of variable size, which grants greater network flexibility.
• Subnets are networks nested within larger networks of a fixed class (A, B, or C).
• Subnet masks are used to guide routers and other network devices in routing IP packets to the correct subnet.
• The subnet mask is a 32-bit number indicating how many bits in an IP address define the subnet, with 1 for network ID and 0 for host ID.
• Default subnet masks are pre-defined for each IP class (e.g., 255.0.0.0 for Class A).

Network Prefixes (CIDR)

• Offers more flexible IP address-space allocation than traditional class-based scheme.
• Uses slash notation: "address/length".
• 'Length' specifies the number of prefix bits in the address that identify the network.
• Enables concise representation of networks.

IPv6

• A successor to IPv4 due to the limited IPv4 addresses.
• Uses 128-bit addresses, which offer a vast address space.
• Provides various communication types: unicast, multicast, and anycast.
• Supports a significantly larger amount of networks than IPv4.
• More efficient use of IP addresses compared to IPv4, resulting in improved efficiency for network operations.
• Uses a hexadecimal notation, which utilizes colon separators to group numeric data into 16-bit blocks.
• Allows for more efficient and comprehensive configuration and support for larger networks.

Types of Communication in IPv6

• Unicast: one-to-one communication; data is sent from one device to another.
• Multicast: one-to-many communication; data is sent to a group of devices.
• Anycast: one-to-nearest communication; data is sent to the geographically closest device among a group of devices.

Subnetting Example

• Different subnetting calculations result in varying numbers of possible subnets and hosts.

Reserved Addresses

• Specific IPv4 address blocks are designated for special purposes.
• Addresses 0.0.0.0/8 are for self-identification.
• Addresses 127.0.0.0/8 and 169.254.0.0/16 are for loopback and link-local networks.
• Private networks (10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16) are not directly connected to the global Internet.
• IPv6 addresses are not reserved for loopback and link-local purposes, but special notation may be part of their specification.

Network Services

• Directory Service: manages and stores information about network resources; examples include LDAP and Active Directory.
• Name Service: maps network resources to their names or addresses; examples include DNS and WINS (Windows Internet Name Service).
• Domain Name System (DNS): hierarchical distributed database that maps domain names to IP addresses.

Dynamic Host Configuration Protocol (DHCP)

• An important protocol that dynamically assigns IP addresses to network devices.
• Simplifies network administration and eliminates manual configuration.
• Four-step process to assign an IP address dynamically.