IP-адреса | Курс "Компьютерные сети"

Introduction to IP Addresses in Networks

Types of IP Addresses

• The lecture introduces two types of addresses used in telecommunications: local and global addresses. Local addresses are tied to specific technologies, such as MAC addresses in Ethernet or cellular networks.

• Local addresses cannot be utilized for constructing large composite networks that integrate different technologies. This limitation is addressed by the network layer in the Open Systems Interconnection (OSI) model, which employs global addresses.

Global Addresses and Their Importance

• Global IP addresses are not technology-dependent and facilitate the creation of networks that connect subnets built on various link-layer technologies, enabling data transfer between these networks.

• These global IP addresses uniquely identify computers within extensive composite networks like the Internet, which consists of diverse parts built on different link-layer technologies.

Versions of IP Protocol

• There are two versions of the Internet Protocol: IPv4 and IPv6. The focus will primarily be on IPv4, while IPv6 will be covered in separate lectures.

• The main distinction between these protocols lies in address length: IPv4 uses 32 bits (4 bytes), whereas IPv6 utilizes 128 bits (16 bytes).

Structure of an IPv4 Address

Breakdown of an IPv4 Address

• An IPv4 address consists of four octets (8 bits each), totaling 32 bits. Each octet is represented in decimal format for ease of use, separated by dots.

• Subnetting is introduced as a method to group multiple computers sharing the same higher-order part of their IP address. In this context, routers operate with subnets rather than individual IP addresses.

Understanding Subnetting

• An IP address comprises two parts: the subnet number (higher-order bits) and the host number (lower-order bits). For example, the first three octets represent the subnet address while the last octet identifies individual hosts within that subnet.

Subnet Masks

Functionality and Representation

• A subnet mask indicates where in an IP address resides the network portion versus the host portion. It also consists of 32 bits; ones indicate network bits while zeros denote host bits.

• To determine a network's address from an IP address using a subnet mask, a logical AND operation is performed between them. This process helps isolate network information from host details.

Notation Formats for Subnet Masks

• Subnet masks can be expressed either in decimal notation or prefix notation. Decimal representation resembles an IP format with four octets separated by dots (e.g., 255.255.255.0).

• Prefix notation specifies how many leading bits belong to the network part; for instance, /24 indicates that the first 24 bits correspond to the network address while remaining bits pertain to hosts.

Variable Length Subnet Masks

Flexibility with Masking Techniques

• While traditional masks often align with octet boundaries for convenience, variable-length subnet masks allow more flexibility by not adhering strictly to these boundaries—enabling efficient use of available addressing space based on specific needs.

• Using prefix lengths like /20 allows defining more granular subnets without being confined to standard sizes, thus optimizing resource allocation across larger networks.

Understanding IP Addressing and Subnetting

Basics of IP Addressing

• The third octet in an IP address can differ from the subnet address due to the last bit being set to one, which does not fall within the subnet mask that only includes the first four bits.

• Modern subnet masks help identify where in an IP address the network part is located versus the host part, moving away from older class-based addressing methods.

Class-Based Addressing System

• The entire range of IP addresses was divided into five classes (A, B, C, D, E), each with a strict definition of network and host addresses.

• Class A includes addresses starting with 0; it allocates 1 byte for the network and 3 bytes for hosts. Class B starts with binary '10', using 2 bytes for networks and 2 bytes for hosts.

Characteristics of Common Classes

• Class C is prevalent among small networks, beginning with '110' in binary. It reserves 24 bits for network identification and only 8 bits for hosts, accommodating up to 254 computers.

• Class D is designated for multicast addresses while Class E remains reserved for future use. Group IP addresses are still allocated from this range.

Structure of IPv4 Addresses

• IPv4 addresses consist of two parts: the subnet number and host number. Each address is represented as four decimal octets separated by dots.