IP Addresses and Subnetting

IP Addresses

All devices connected to the Internet use either a 32-bit IPv4 address or a 128-bit IPv6 address. Think of the IP address as a logical address (possibly temporary), while the 48-bit address on every NIC is the physical (permanent) address.

• IPv4: 32-bit binary address, often written in dotted decimal notation for readability.
• IPv6: 128-bit binary address, offering a larger address space for more devices.

IP Subnet Masking

When you have many IP addresses to manage, subnet masking helps break the host ID portion into a subnet ID and a host ID.

Example: Applying a subnet mask of 255.255.255.0 to a Class B address will split the 16-bit host ID into an 8-bit subnet ID and an 8-bit host ID.

Classless IP Addressing

Today, most addresses are classless. Instead of applying for a specific class of IP addresses, companies lease blocks of IP addresses from ISPs. This leads to more efficient allocation of addresses.

Example: Instead of applying for two Class C addresses, a company may lease 500 IP addresses from an ISP, as a contiguous block of addresses.

Subnetting

Subnetting allows a network to be divided into smaller subnets.

Need for Subnetting:

• Classes A and B allow a large number of hosts per network, but it may be necessary to subdivide networks for better management and efficiency.

Principle: Use parts of the host IDs for creating subnets. A subnet mask facilitates traffic between subnets and the external network.

Example:

• Subnet mask: 255.255.255.0
• Address: 192.168.1.0
• Breaks the network into subnets with smaller broadcast domains.

Slash Notation (CIDR)

In slash notation, the number after the slash represents the number of bits allocated to the network ID.

Example:

• IP address: 167.199.170.82/27
• This means 27 bits are for the network ID and 5 bits are for the host ID.
• Subnet mask: 255.255.255.224 (in binary: 11111111.11111111.11111111.11100000)
• The network contains 32 addresses.

First and Last Address:

• First Address: AND the IP address with the subnet mask.
  • IP: 10100111 11000111 10101010 01010010
  • Mask: 11111111 11111111 11111111 11100000
  • Result: 167.199.170.64/27 (network address)
• Last Address: 31 addresses after the first.
  • Last address: 167.199.170.95/27 (broadcast address).