Subnetting Basics and Classes

Subnet Masks

• Subnetting is a technique used to divide networks into smaller networks called subnets.
• Subnet masks identify which bits in an IP address represent the network/subnet portion.
• Subnets are created by borrowing bits from the host portion of the IP address.
• Routers use this information to direct data packets to the correct subnet.

Subnetting - Class A, B, and C

• IPv4 addresses are divided into classes (A, B, and C).
• Each class has a different network and host bit structure.
• Class A networks have the most host bits, enabling a large number of hosts.
• Class C networks have the fewest host bits, allowing for smaller networks.

Borrowing Bits

• Subnets are created by borrowing bits from the host portion of the IP address.
• The number of subnets that can be created depends on the number of bits borrowed.
• The more bits borrowed, the smaller the subnet size and the fewer hosts per subnet.

Number of Subnets and Hosts

• The formula for calculating the number of subnets is 2^x, where x is the number of bits borrowed.
• The formula for calculating the number of hosts per subnet is 2^y-x - 2, where y is the number of host bits for a specific class network.
• The class number dictates how many bits are used for the host portion of the address.

Subnet Mask and Network/Subnet Bits

• A subnet mask is a 32-bit value that designates which bits in an IP address represent the network portion and which represent the host portion.
• A "1" bit in the subnet mask signals a network or subnet bit.
• A "0" bit signifies a host bit.

Logical AND operation

• Computers use a logical AND operation to determine if a destination IP address is on the same LAN.
• Setting a subnet mask bit to '1' allows data packet bits to pass.
• Applying a zero in the subnet mask effectively filters that bit from output.

Network and Broadcast Addresses

• Each subnet has a unique network address and a broadcast address.
• The network address identifies the subnet.
• The broadcast address is used to transmit data packets to all hosts within a subnet.

Example Subnet Calculation

• Given a Class C network (192.168.12.0), borrowing two bits can create four subnets (2²).
• Each subnet would then have 64 hosts per subnet (2^8-2 -2)

Example 6-8

• Given a network address (10.0.0.0).
• Divide the network into 8 subnets.
• Specify the subnet mask (255.224.0.0) that creates the subnets.
• Calculate the broadcast addresses for each of the 8 subnets.
• Calculate the number of usable hosts per subnet.

Example 6-9

• Determine the subnet mask required for a router-router link (172.16.31.1, 172.16.31.2).

• Only two host addresses are required .

• The subnet mask is (255.255.255.252)

• Subnet Mask in Data Flow Control

• The subnet mask helps guide data packets in a network to either a designated host on the LAN, or a gateway.

• The gateway is usually a Layer 3 router or switch.

Summary

• The material presented covers the concept of subnetting, and its use in defining networks and subnet masks for controlling how data is transmitted across different networks.
• Detailed examples and calculations help students grasp the process of borrowing bits, determining the number of hosts per subnet, and identifying subnet masks for use in data traffic.

This quiz covers the fundamentals of subnetting, including subnet masks, the classification of IPv4 addresses, and the concept of borrowing bits from host portions. It explores how different classes (A, B, C) affect the number of available subnets and hosts within a network. Test your understanding of these key concepts in subnetting!