Subnetting

Nerd Cafe

Step 1: Understand the Original Network

• IP Range: 192.168.1.0/24

• CIDR Notation (/24): This means the first 24 bits are the network portion, leaving 8 bits for hosts (32 total bits - 24 network bits = 8 host bits).

• Total Addresses: With 8 host bits, the network has 2^8 = 256 addresses (from 192.168.1.0 to 192.168.1.255).

• Usable Addresses: 256 - 2 (network and broadcast addresses) = 254 usable host addresses.

Step 2: Determine Subnet Requirements

• We need 5 subnetworks.

• Use the formula $2^{n}\ge subnets$, where n is the number of bits we borrow from the host portion to create subnets.

• Calculate n:

  • $2^{2}=4$, (not enough, as 4 < 5).

  • $2^{3}=8$, (sufficient, as 8 ≥ 5).

• Therefore, we need 3 bits for subnetting (n = 3).

Step 3: Calculate the New Subnet Mask

• Original subnet mask: /24 (255.255.255.0).

• Borrow 3 bits from the host portion: 24 + 3 = /27.

• New subnet mask in decimal:

  • /27 means 27 bits are 1s in the subnet mask.

  • Binary: 11111111.11111111.11111111.11100000

  • Decimal: 255.255.255.224 (since 11100000 = 128 + 64 + 32 = 224).

Step 4: Calculate Number of Subnets and Hosts per Subnet

• Number of Subnets: With 3 bits borrowed, we get $2^{3}=8$ subnets (we only need 5, so 3 will be unused).

• Host Bits Remaining: Original 8 host bits - 3 borrowed bits = 5 host bits.

• Addresses per Subnet: $2^{5}=32$ addresses per subnet.

• Usable Hosts per Subnet: 32 - 2 (network and broadcast) = 30 usable hosts.

Step 5: Calculate Subnet Address Increments

• The subnet mask /27 has 32 addresses per subnet.

• The increment is determined by the last octet of the subnet mask (224):

  • 256 - 224 = 32. Each subnet increments by 32 in the fourth octet.

Step 6: List the Subnets

Starting from 192.168.1.0, we increment the fourth octet by 32 for each subnet. Here are the first 5 subnets:

1. Subnet 1:

   • Network Address: 192.168.1.0

   • Usable Range: 192.168.1.1 to 192.168.1.30

   • Broadcast Address: 192.168.1.31

   • Subnet Mask: 255.255.255.224 (/27)

2. Subnet 2:

   • Network Address: 192.168.1.32 (0 + 32)

   • Usable Range: 192.168.1.33 to 192.168.1.62

   • Broadcast Address: 192.168.1.63

   • Subnet Mask: 255.255.255.224 (/27)

3. Subnet 3:

   • Network Address: 192.168.1.64 (32 + 32)

   • Usable Range: 192.168.1.65 to 192.168.1.94

   • Broadcast Address: 192.168.1.95

   • Subnet Mask: 255.255.255.224 (/27)

4. Subnet 4:

   • Network Address: 192.168.1.96 (64 + 32)

   • Usable Range: 192.168.1.97 to 192.168.1.126

   • Broadcast Address: 192.168.1.127

   • Subnet Mask: 255.255.255.224 (/27)

5. Subnet 5:

   • Network Address: 192.168.1.128 (96 + 32)

   • Usable Range: 192.168.1.129 to 192.168.1.158

   • Broadcast Address: 192.168.1.159

   • Subnet Mask: 255.255.255.224 (/27)

Cisco Packet Tracer (Version 6.2.0.0052)

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subnetting.pkt