IPv4 Addressing

IPv4 addressing identifies devices and networks so packets can be delivered. Understanding IPv4 structure, address types, and subnetting is essential for building and troubleshooting networks.

An IPv4 address is 32 bits long and is usually written in dotted decimal format.

Example:

192.168.10.25

Each decimal number represents 8 bits, called an octet. Therefore, an IPv4 address has four octets.

192      .168      .10       .25
11000000 .10101000 .00001010 .00011001

A subnet mask or prefix length identifies which part of the address is the network portion and which part is the host portion.

Each IPv4 network includes special addresses.

For 192.168.1.0/24, the network address is 192.168.1.0, usable host addresses are 192.168.1.1 through 192.168.1.254, and the broadcast address is 192.168.1.255.

IPv4 addresses may be public or private.

Private addresses are used inside organizations and homes. They are not routed directly on the public internet. Network Address Translation (NAT) is commonly used when private hosts access the internet.

Other special address categories include loopback addresses, link-local addresses, and experimental or reserved ranges.

IPv4 addresses can be assigned manually or automatically.

Static addressing is common for routers, servers, printers, and infrastructure devices. DHCP is common for user devices.

Network segmentation divides a larger network into smaller subnets. Segmentation helps improve organization, security, broadcast control, and address management.

Subnetting borrows bits from the host portion to create additional network bits.

A prefix length shows how many bits are used for the network portion.

Usable hosts are calculated as:

2^(host bits) - 2

The subtraction accounts for the network address and broadcast address.

Requirement: Split 192.168.1.0/24 into four equal subnets.

Borrow 2 host bits because 2^2 = 4. The new prefix is /26.

Variable Length Subnet Masking (VLSM) allows different subnet sizes inside the same larger address block. This saves addresses because each subnet can be sized according to need.

A common VLSM strategy is to assign the largest subnet first, then continue with smaller requirements.