Subnetting 192.168.2.0/24 into Subnets of 48 Hosts Each

Given Data

• Network: $192.168.2.0/24$
• Required hosts per subnet: $48$

Step 1: Host Bits Required

Need $2^n - 2 \geq 48$:

So host bits = 6.

Step 2: Subnet Mask / New Prefix

• Total bits = 32, original network bits = 24
• Borrowed subnet bits = $32 - 24 - 6 = 2$
• New prefix = $/24 + 2 = /26$

Fourth octet: $11000000_2 = 192$

Subnet Mask = 255.255.255.192 (/26)

Step 3: Number of Subnets and Block Size

• Subnets = $2^2 = 4$
• Block size (increment) = $2^6 = 64$
• Usable hosts per subnet = $2^6 - 2 = 62$ (≥ 48 ✓)

Step 4: Subnet Table

Step 5: Network Ranges

Advantages of Subnetting

1. Efficient IP address utilization - reduces address wastage by sizing blocks appropriately.
2. Reduced broadcast traffic / smaller broadcast domains - improves performance.
3. Improved network performance - less congestion within segments.
4. Enhanced security - inter-subnet traffic passes through routers where access control can be applied.
5. Easier management and troubleshooting - logical, smaller segments.
6. Scalability - new subnets added without full redesign.

Domain Name System (DNS)

Major Purpose of DNS

The major purpose of DNS (Domain Name System) is to translate human-readable domain names into machine-readable IP addresses (and vice versa).

Since computers communicate using numerical IP addresses (e.g., 192.168.1.1), but humans find it easier to remember names (e.g., www.google.com), DNS acts as a distributed hierarchical naming system that maps domain names to their corresponding IP addresses automatically, without requiring users to memorize numeric addresses.

How DNS Resolves a Domain Name

DNS resolution follows a step-by-step hierarchical query process:

DNS Resolution Steps

Example: Resolving www.example.com

Step 1: Browser Cache Check

• The user types www.example.com in the browser.
• The browser first checks its local cache to see if the IP address is already stored from a previous visit.

Step 2: OS / Local Hosts File Check

• If not found in browser cache, the OS checks the local hosts file and its own DNS cache.

Step 3: Query to Recursive Resolver (Local DNS Server)

• If still unresolved, the query is sent to the Recursive Resolver (usually provided by the ISP or configured manually, e.g., 8.8.8.8).
• The recursive resolver takes responsibility for finding the answer.

Step 4: Query to Root Name Server

• The recursive resolver contacts a Root Name Server (there are 13 sets globally).
• The root server does not know the IP of www.example.com, but it refers the resolver to the TLD (Top-Level Domain) Name Server for .com.

Step 5: Query to TLD Name Server

• The resolver queries the TLD Name Server for .com.
• The TLD server responds with the address of the Authoritative Name Server for example.com.

Step 6: Query to Authoritative Name Server

• The resolver queries the Authoritative Name Server for example.com.
• This server holds the actual DNS records and returns the IP address (e.g., 93.184.216.34) for www.example.com.

Step 7: Response Returned to Client

• The recursive resolver caches the result (for the TTL duration) and sends the IP address back to the client.
• The browser then uses the IP address to establish a connection with the web server.

Diagram of DNS Resolution

Client
  |
  v
Recursive Resolver (ISP/Local DNS)
  |
  v
Root Name Server  --> "Go to .com TLD server"
  |
  v
TLD Name Server (.com)  --> "Go to example.com Authoritative server"
  |
  v
Authoritative Name Server (example.com)  --> Returns IP address
  |
  v
Recursive Resolver --> Client (IP delivered)

Summary Table

Note: DNS primarily uses UDP port 53 for queries and TCP port 53 for zone transfers.