Subnetting Class A Networks
Scenario: Given a 10.0.0.0/8 network, you need to create 2000 subnets.
Prefix Length Calculation:
-
To determine the prefix length needed for 2000 subnets, calculate the number of bits required:
- (2^{10} = 1024) (not enough)
- (2^{11} = 2048) (sufficient)
Therefore, you need to borrow 11 bits from the host portion, resulting in a new subnet mask of /19:
- Original Network: 10.0.0.0/8
- Subnet Mask: 255.255.224.0
- New Prefix Length: /19 (8 bits from the original + 11 borrowed bits)
Hosts per Subnet:
- Remaining host bits: 32 - 19 = 13 bits
- Number of hosts: (2^{13} - 2 = 8190) usable hosts per subnet
Variable-Length Subnet Masking (VLSM)
Concept:
- VLSM allows for subnets of varying sizes, optimizing the use of IP addresses compared to Fixed-Length Subnet Masks (FLSM), where all subnets have the same size.
Steps for VLSM:
-
TOKYO LAN A (110 Hosts):
- Required Subnet Size: Enough for 128 hosts ((2^7))
- Subnet Mask: /25
- Network Address: 192.168.1.0/25
- Broadcast Address: 192.168.1.127
- Usable IP Range: 192.168.1.1 - 192.168.1.126
- Total Usable Hosts: 126 (2^7 - 2)
-
TORONTO LAN B (45 Hosts):
- Required Subnet Size: Enough for 64 hosts ((2^6))
- Subnet Mask: /26
- Network Address: 192.168.1.128/26
- Broadcast Address: 192.168.1.191
- Usable IP Range: 192.168.1.129 - 192.168.1.190
- Total Usable Hosts: 62 (2^6 - 2)
-
TORONTO LAN A (29 Hosts):
- Required Subnet Size: Enough for 32 hosts ((2^5))
- Subnet Mask: /27
- Network Address: 192.168.1.192/27
- Broadcast Address: 192.168.1.223
- Usable IP Range: 192.168.1.193 - 192.168.1.222
- Total Usable Hosts: 30 (2^5 - 2)
-
TOKYO LAN B (8 Hosts):
- Required Subnet Size: Enough for 16 hosts ((2^4))
- Subnet Mask: /28
- Network Address: 192.168.1.224/28
- Broadcast Address: 192.168.1.239
- Usable IP Range: 192.168.1.225 - 192.168.1.238
- Total Usable Hosts: 14 (2^4 - 2)
-
Point-to-Point Connection (2 Hosts):
- Required Subnet Size: Enough for 4 hosts ((2^2))
- Subnet Mask: /30
- Network Address: 192.168.1.240/30
- Broadcast Address: 192.168.1.243
- Usable IP Range: 192.168.1.241 - 192.168.1.242
- Total Usable Hosts: 2 (2^2 - 2)
Additional Practice for Subnetting
For more practice and exercises on subnetting, check out the following resources:
- Subnetting Questions
- Subnetting.org
- Subnetting Practice (Preferred site)
Summary
This guide covers how to subnet Class A networks and the concept of VLSM to efficiently allocate IP addresses. Following the steps provided will help you manage IP address allocation and ensure that subnets meet the specific needs of different network segments.