Addressing

Introduction

Addressing in computer networks: mechanism to uniquely identify devices and resources for data delivery. Enables routing, switching, and communication across heterogeneous networks. Types: physical (hardware), logical (software). Crucial for scalability, interoperability, and network management.

"Without addressing, communication in networks becomes impossible; it is the cornerstone of all data exchange." -- Andrew S. Tanenbaum

Addressing Overview

Definition and Purpose

Addressing: assignment of identifiers to network entities. Purpose: enable identification, location, and communication. Supports routing, packet delivery, resource allocation.

Types of Addresses

Physical Address: hardware-based, immutable, Layer 2. Logical Address: software-based, configurable, Layer 3 and above. Port Address: identifies application endpoints.

Addressing Levels

Link Layer: MAC addresses. Network Layer: IP addresses. Transport Layer: port numbers. Application Layer: domain names, URLs.

Physical Addressing

MAC Addresses

Media Access Control (MAC) address: 48-bit unique identifier assigned to NICs. Format: six groups of two hexadecimal digits separated by colons or hyphens (e.g., 00:1A:2B:3C:4D:5E). Purpose: local network identification.

MAC Address Structure

First 24 bits: Organizationally Unique Identifier (OUI). Last 24 bits: NIC-specific identifier. Ensures global uniqueness.

Physical Addressing Role

Used in LAN communication, Ethernet frames, ARP resolution. Immutable by default but can be spoofed. Essential for frame delivery within broadcast domains.

Logical Addressing

Definition

Logical addresses assigned by software, hierarchical, routeable across networks. Examples: IPv4, IPv6 addresses. Dynamic or static assignment possible.

Network Layer Addressing

Enables internetwork communication. Independent of physical hardware. Supports routing decisions based on address prefixes.

Address Allocation

Managed by IANA and regional registries. Mechanisms: DHCP, manual configuration, SLAAC for IPv6. Ensures uniqueness within administrative domains.

IPv4 Addressing

Address Format

32-bit binary number, displayed as four octets in decimal separated by dots (dotted-decimal notation). Example: 192.168.1.1.

Address Classes

Class A, B, C for unicast; Class D for multicast; Class E reserved. Classful addressing deprecated but legacy support persists.

Public vs Private Addresses

Public addresses routable on the internet. Private addresses reserved for internal use (RFC 1918). NAT translates private to public addresses.

IPv4 Address Example Table

IPv6 Addressing

Address Format

128-bit hexadecimal number divided into eight 16-bit blocks separated by colons. Example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334.

Address Types

Unicast: one interface. Anycast: nearest interface in group. Multicast: multiple interfaces. No broadcast address in IPv6.

Address Abbreviation Rules

Leading zeros omission. Consecutive zero blocks replaced by :: once per address. Improves readability.

IPv6 Address Example Table

Subnetting

Concept

Subnetting: dividing a network into smaller subnetworks. Improves address utilization, reduces broadcast domains, enhances security and performance.

Subnet Masks

Defines network and host portions of IP address. Expressed in dotted-decimal or CIDR notation (e.g., 255.255.255.0 or /24).

Subnet Calculation

Number of subnets: 2^n, where n = borrowed bits. Number of hosts per subnet: 2^h - 2, where h = remaining host bits.

Given:IP address: 192.168.1.0Subnet mask: 255.255.255.192 (/26)Calculation:- Borrowed bits (n): 2 (since 192 = 11000000)- Number of subnets: 2^2 = 4- Hosts per subnet: 2^(32-26) - 2 = 62

Applications

Used to organize networks, optimize IP usage, isolate traffic for security, and improve routing efficiency.

Address Resolution Protocol (ARP)

Purpose

Translates logical IP addresses to physical MAC addresses. Essential for Ethernet communication in IPv4 networks.

Operation

Broadcasts ARP request for IP to MAC mapping. Receives ARP reply with MAC address. Stores mapping in ARP cache.

ARP Packet Structure

Includes hardware type, protocol type, hardware size, protocol size, opcode, sender MAC/IP, target MAC/IP.

ARP Packet Fields:- Hardware Type (HTYPE)- Protocol Type (PTYPE)- Hardware Size (HLEN)- Protocol Size (PLEN)- Operation (OPER): request or reply- Sender Hardware Address (SHA)- Sender Protocol Address (SPA)- Target Hardware Address (THA)- Target Protocol Address (TPA)

Limitations

Vulnerable to spoofing attacks. Limited to broadcast domain. IPv6 uses Neighbor Discovery Protocol (NDP) instead.

Domain Name System (DNS)

Role in Addressing

Translates human-readable domain names to IP addresses. Enables user-friendly resource access.

DNS Hierarchical Structure

Root servers, top-level domains (TLDs), authoritative name servers. Distributed database model.

DNS Query Types

Recursive: client requests complete answer. Iterative: server returns best possible info. Types: A (IPv4), AAAA (IPv6), CNAME, PTR, MX.

DNS Resolution Process

Client sends query → resolver → root server → TLD server → authoritative server → IP returned.

Addressing Schemes

Unicast

One-to-one communication. Unique address per interface. Standard for most network traffic.

Multicast

One-to-many communication. Group addresses used to send packets to multiple receivers simultaneously.

Broadcast

One-to-all communication within a subnet. IPv4 supports broadcast; IPv6 does not.

Anycast

One-to-nearest communication. Same address assigned to multiple nodes; packet delivered to closest.

Routing and Addressing

Address Role in Routing

Logical addresses used to forward packets through interconnected networks. Routers examine destination address to determine next hop.

Hierarchical Addressing

Network portion identifies subnet or network. Host portion identifies specific device. Simplifies routing tables and aggregation.

Routing Protocols

Protocols (e.g., OSPF, BGP) use addressing to build routing tables. Address prefixes advertise network reachability.

Address Aggregation

Combines multiple routes into single entry. Reduces routing table size. Enabled by CIDR and hierarchical addressing.

Security in Addressing

Address Spoofing

Attacker falsifies IP or MAC address to masquerade as trusted device. Enables man-in-the-middle, DoS attacks.

Mitigation Techniques

Packet filtering, ingress/egress filtering, dynamic ARP inspection, IPsec for authentication.

Address Privacy

IPv6 privacy extensions generate temporary addresses to prevent tracking. DHCP logs aid auditing.

Access Control

Network ACLs restrict access based on addresses. Firewalls and VPNs enforce address-based policies.

References

• Andrew S. Tanenbaum, David J. Wetherall, "Computer Networks," 5th ed., Pearson, 2011, pp. 112-157.
• Douglas E. Comer, "Internetworking with TCP/IP Volume One," 6th ed., Prentice Hall, 2013, pp. 89-135.
• W. Richard Stevens, "TCP/IP Illustrated, Volume 1: The Protocols," Addison-Wesley, 1994, pp. 201-245.
• K. Obraczka, "Multicast Addressing and Routing," IEEE Communications Magazine, vol. 36, no. 1, 1998, pp. 98-105.
• R. Hinden, S. Deering, "IP Version 6 Addressing Architecture," RFC 4291, 2006, pp. 1-29.