Overview
This lecture covers IPv4 address classes, their default subnet masks, how to identify address classes, and the calculation of key subnet values.
IPv4 Address Classes
- IPv4 addresses were divided into five classes: A, B, C, D, and E.
- Class A uses 8 bits for network and 24 bits for host (default mask 255.0.0.0).
- Class B uses 16 bits for network and 16 bits for host (default mask 255.255.0.0).
- Class C uses 24 bits for network and 8 bits for host (default mask 255.255.255.0).
- Class D addresses (224-239) are reserved for multicast, not individual devices.
- Class E addresses (240-255) are reserved and not used for public addressing.
- Class-based addressing is outdated since 1993 but still used as a reference.
Identifying an Address's Class
- Class A: First octet 0–127 (first bit 0).
- Class B: First octet 128–191 (first bits 10).
- Class C: First octet 192–223 (first bits 110).
- Class D: First octet 224–239 (first bits 1110).
- Class E: First octet 240–255 (first bits 1111).
Examples of Address Classification
- 17.x.x.x: Class A
- 220.x.x.x: Class C
- 165.x.x.x and 128.x.x.x: Class B
- 191.x.x.x: Class B
- 192.x.x.x: Class C
Key Subnet Values and Calculation
- Four key values for each subnet: Network Address, First Host, Broadcast Address, Last Host.
- Network Address: Set all host bits to zero.
- First Host: Network Address plus one.
- Broadcast Address: Set all host bits to one.
- Last Host: Broadcast Address minus one.
- Example for Class A (10.x.x.x): Network=10.0.0.0, First Host=10.0.0.1, Broadcast=10.255.255.255, Last Host=10.255.255.254.
- Example for Class B (172.16.x.x): Network=172.16.0.0, First Host=172.16.0.1, Broadcast=172.16.255.255, Last Host=172.16.255.254.
- Example for Class C (192.168.4.x): Network=192.168.4.0, First Host=192.168.4.1, Broadcast=192.168.4.255, Last Host=192.168.4.254.
Key Terms & Definitions
- IP Address — A unique identifier for a device on a network.
- Subnet Mask — A number that divides the IP address into network and host parts.
- Network Address — The ID that identifies a specific subnet.
- Broadcast Address — The last address in a subnet, used to send messages to all devices in the subnet.
- Host Address — The part of the IP used to identify devices within the subnet.
- Classful networking — Original scheme for dividing IP address space into classes.
Action Items / Next Steps
- Review IP address classes and their default subnet masks.
- Practice calculating subnet key values using network and host bits.
- Prepare for further study on advanced subnetting techniques.