Lecture-2-IP Subnetting, Troubleshooting IP, and NAT

Computer Network & Communication Notes

1. Concepts and Characteristics of Routing and Switching

• Understanding routing and switching is essential for network management.

• Routing: Determines the best path for data packets to travel across networks.

• Switching: Connects devices on a same network, creating a local area network (LAN).

2. Subnetting

2.1 Subnetting Basics

• Definition: Subnetting divides a larger network into smaller, manageable networks.

• Need for Subnetting: Necessary when one network address is to be split into several networks.

2.2 Benefits of Subnetting

• Reduced Network Traffic: Routers manage traffic effectively, limiting broadcast domains to reduce congestion.

• Optimized Network Performance: Less congestion leads to better overall performance.

• Simplified Management: Easier to identify and troubleshoot problems.

• Facilitated Spanning across Distances: Smaller networks are more efficient over slower WAN links.

3. How to Create Subnets

• Subnets are created by borrowing bits from the host portion of an IP address, which reduces host availability but increases subnet quantity.

4. Subnet Masks

• Definition: A 32-bit value that differentiates the network segment from the host segment in an IP address.

• Example: A subnet mask comprises a series of 1s (network) and 0s (host).

5. Classless Inter-Domain Routing (CIDR)

• CIDR Definition: Method for allocating IP addresses, allowing flexibility in how addresses are grouped.

• **Default Subnet Masks:

  • Class A: 255.0.0.0 (/8)

  • Class B: 255.255.0.0 (/16)**

5.1 CIDR Values Table

6. Subnetting Class C Addresses

• Host Bits: In Class C, only 8 bits are available for hosts.

• Subnet Masks: Must be calculated without skipping bits.

6.1 Fast Method for Subnetting Class C

• Answer these questions to subnet efficiently:

  1. How many subnets?

  2. Hosts per subnet?

  3. Valid subnets?

  4. Broadcast address per subnet?

  5. Valid hosts per subnet?

7. Practice Examples

• Class C Example: Subnet mask 255.255.255.128

  • Subnets: 2

  • Valid Hosts: 126

  • Valid subnets: 0, 128

  • Broadcast addresses: 127 (for 0 subnet)

8. Subnetting Class B Addresses

• Class B offers broader subnetting options compared to Class C.

• Example:

  • Network Address: 172.16.0.0

  • Subnet Mask: 255.255.128.0

  • Hosts: 32,766,

  • Subnets: 2

9. Troubleshooting IP Addressing

• Start with basic checks: ping local address (127.0.0.1) to check IP stack initialization.

• Ping local IP and default gateway to troubleshoot connectivity.

9.1 Common Troubleshooting Commands

• Ping: Test IP connectivity (ICMP protocol).

• Traceroute: Map routes taken by packets.

• arp -a: Shows IP-to-MAC mappings.

• ipconfig /all: Displays detailed IP configuration information.

10. Introduction to Network Address Translation (NAT)

• Purpose: Allows multiple private IPs to share a public IP address, conserving address space.

• Useful when merging networks or changing ISPs.

10.1 Types of NAT

• Static NAT: One-to-one mapping for each internal host.

• Dynamic NAT: Maps unregistered IPs to registered from a pool.

• Overloading (PAT): Many-to-one mapping using port numbers to distinguish traffic.

11. NAT Functionality

• Translation Process: Outbound packets are modified by NAT router, keeping a NAT table for tracking.

• Allows multiple hosts to use one public IP by using ports for identification.