Introduction to Subnetting and CIDR Notation

Introduction to Subnetting

• Subnetting divides a large IP network into smaller, more manageable subnets.
• This improves network performance and security.
• It enhances organization and control of network resources.
• Each subnet has a unique subnet mask.
• Administrators use subnets to efficiently allocate IP addresses and logically group the network.

Subnet Masks

• Subnet masks define subnet boundaries within an IP address.
• They are 32-bit values combined with IP addresses to identify network and host portions.
• Typically expressed in dotted decimal notation (e.g., 255.255.255.0).
• The mask determines which IP address bits represent the network and host.
• A /24 subnet mask is equivalent to 255.255.255.0.

CIDR Notation

• Classless Inter-Domain Routing (CIDR) provides standardizing representation for IP addresses and masks.
• It uses a slash followed by a number (e.g., /24) to represent the mask.
• The number indicates leading 1 bits in the subnet mask.
• CIDR clarifies network structure and simplifies subnetting.

Calculating Subnets

• Determining the number of subnets and hosts involves bit manipulation.
• The subnet mask defines network and host bits.
• Calculations for hosts and subnets depend on the mask's host bits.

Subnet Address Calculation

• The subnet address comes from the network address and subnet mask.
• Find the network address by performing a logical AND operation between the IP address and the mask.
• This reveals the subnet the IP belongs to.
• This calculation is key for network routing and communication.

Finding the Broadcast Address

• The broadcast address is the highest IP address in a subnet.
• It sends data to all hosts within the subnet.
• Calculated by adding the maximum possible host address to the network address.

Determining the Number of Subnets and Hosts

• The number of subnets depends on bits borrowed from the host portion for the subnet ID.
• The formula for calculating subnets is 2ⁿ, where n is the number of borrowed bits.
• The maximum usable hosts in a subnet is 2^p - 2, where p = number of bits left for host addresses.

Varying Subnet Masks

• Different subnet masks offer varying numbers of hosts and subnets.
• A /24 has fewer subnets but more hosts per subnet compared to a /16.
• The subnet mask's choice significantly impacts network design, administration, and efficiency.

Practical Applications of Subnetting

• Subnetting organizes larger networks into smaller logical units.
• Improved IP address management and network resource control.
• It enhances routing efficiency and performance.
• Proper subnetting boosts network security by isolating networks to prevent unauthorized access and minimize attack surfaces.