Understanding IP Addressing and Subnetting

In networking, IP addressing is fundamental to routing and identifying devices on a network. IP addresses come in two major versions: IPv4 and IPv6. While IPv6 is gaining traction, IPv4 is still widely used. This article explores IPv4 addressing, subnetting, and provides some practical examples.

1. Physical vs Logical Addressing

Physical Addressing (MAC Address):
- The MAC (Media Access Control) address is a unique identifier assigned to a network interface card (NIC) for communication on the physical network segment.
- Format: 48-bit address represented in hexadecimal, e.g., 00:1A:2B:3C:4D:5E.
Logical Addressing (IP Address):
- IPv4: A 32-bit logical address divided into 4 octets. Each octet ranges from 0 to 255. Example: 192.168.39.240.
- IPv6: A 128-bit logical address used for the next generation of IP addressing, providing a vastly larger address space.

2. IPv4 Address Classes

IPv4 addresses are categorized into different classes, primarily A, B, C, D, and E:

Class A:
- Range: 1.0.0.0 to 126.0.0.0
- Default Subnet Mask: 255.0.0.0
- Structure: N.H.H.H (N=Network, H=Host)
Class B:
- Range: 128.0.0.0 to 191.255.0.0
- Default Subnet Mask: 255.255.0.0
- Structure: N.N.H.H
Class C:
- Range: 192.0.0.0 to 223.255.255.255
- Default Subnet Mask: 255.255.255.0
- Structure: N.N.N.H
Class D:
- Range: 224.0.0.0 to 239.255.255.255
- Usage: Multicasting
Class E:
- Range: 240.0.0.0 to 255.255.255.255
- Usage: Reserved for research and future use
Special Address:
- 127.0.0.1: Loopback address used for testing and troubleshooting on a local machine.

3. Subnetting

Subnetting is the process of dividing a network into smaller, more manageable sub-networks (subnets). This helps in optimizing the use of IP addresses and improving network performance.

Subnet Masks

A subnet mask is a 32-bit number that segments an IP address into network and host portions. For example:

Class A Default Subnet Mask: 255.0.0.0
Class B Default Subnet Mask: 255.255.0.0
Class C Default Subnet Mask: 255.255.255.0

Binary Conversion Example

To better understand how IP addresses are manipulated in subnetting, converting them to binary is crucial:

IP Address: 192.168.37.200
Binary Conversion:
- 192: 11000000
- 168: 10101000
- 37: 00100101
- 200: 11001000

Thus, 192.168.37.200 in binary is 11000000.10101000.00100101.11001000.

4. Private IP Address Ranges

Private IP addresses are used within a private network and are not routable on the public internet. Common ranges include:

Class A: 10.0.0.0 to 10.255.255.255
Class B: 172.16.0.0 to 172.31.255.255
Class C: 192.168.0.0 to 192.168.255.255

5. Network and Broadcast IDs

Each subnet has a Network ID and a Broadcast ID:

Network ID: The first address in the subnet, used to identify the network itself.
Broadcast ID: The last address in the subnet, used to send data to all devices within the network.

Example with the IP 150.10.20.30 in a Class B network:

Network ID: 150.10.0.0
Broadcast ID: 150.10.255.255
Number of Usable Hosts: 2^16 - 2 = 65,534

6. Practical Subnetting Example

Let's tackle this subnetting problem step by step, starting with Class C and then moving to Class A.

Problem Overview:

We need to subnet a network to create subnets that can support at least 40 hosts each.

Step 1: Subnetting a Class C Network

Original Network:

Address: 197.10.10.0/24
Default Subnet Mask: 255.255.255.0

Step 1.1: Calculate the Number of Bits for Subnetting

Hosts Requirement: At least 40 hosts per subnet.
Host Bits Calculation:
- We need at least 6 bits for the host portion since (2^6 = 64) (where 64 - 2 = 62 usable hosts).

Thus, we’ll use the following subnet mask:

Subnet Mask: 255.255.255.192 (/26)

Step 1.2: Create Subnets

We now divide the network into smaller subnets using the /26 subnet mask:

Total Subnets: With 2 bits borrowed for subnetting, (2^2 = 4) subnets are created.
Hosts per Subnet: (2^6 - 2 = 62) usable hosts per subnet.

Here are the subnets:

1st Subnet:
- Network ID: 197.10.10.0/26
- Range: 197.10.10.0 to 197.10.10.63
- Broadcast Address: 197.10.10.63
2nd Subnet:
- Network ID: 197.10.10.64/26
- Range: 197.10.10.64 to 197.10.10.127
- Broadcast Address: 197.10.10.127
3rd Subnet:
- Network ID: 197.10.10.128/26
- Range: 197.10.10.128 to 197.10.10.191
- Broadcast Address: 197.10.10.191
4th Subnet:
- Network ID: 197.10.10.192/26
- Range: 197.10.10.192 to 197.10.10.255
- Broadcast Address: 197.10.10.255

Conclusion for Class C:

Limitation: While we successfully created 4 subnets, each supporting 62 hosts, a Class C network is limited in the number of subnets and hosts it can support. If you need more subnets or more hosts per subnet, a Class C address might not be sufficient.

Step 2: Subnetting a Class A Network

Let's apply the same logic to a Class A address.

Original Network:

Address: 12.0.0.0/8
Default Subnet Mask: 255.0.0.0

Step 2.1: Calculate the Number of Bits for Subnetting

Hosts Requirement: Again, we need at least 40 hosts per subnet.
Host Bits Calculation:
- As before, we need 6 bits for the host portion, leaving 26 bits for the network portion.

Thus, the subnet mask is:

Subnet Mask: 255.255.255.192 (/26)

Step 2.2: Create Subnets

A Class A network offers significantly more flexibility and addresses. Let's create some subnets within the 12.0.0.0/8 range using a /26 subnet mask:

1st Subnet:
- Network ID: 12.0.0.0/26
- Range: 12.0.0.0 to 12.0.0.63
- Broadcast Address: 12.0.0.63
2nd Subnet:
- Network ID: 12.0.0.64/26
- Range: 12.0.0.64 to 12.0.0.127
- Broadcast Address: 12.0.0.127
3rd Subnet:
- Network ID: 12.0.0.128/26
- Range: 12.0.0.128 to 12.0.0.191
- Broadcast Address: 12.0.0.191
4th Subnet:
- Network ID: 12.0.0.192/26
- Range: 12.0.0.192 to 12.0.0.255
- Broadcast Address: 12.0.0.255

Conclusion for Class A:

A Class A address provides an enormous number of subnets and hosts per subnet, making it more suitable for larger networks.
Advantages: You can create many more subnets with a large number of hosts each, and even larger networks can be easily accommodated.