IP Subnetting Overview

IP Subnetting

• IP subnetting is a logical division of one large network into several smaller networks.
• This improves management, performance, and security.
• Subnetting necessitates routers to connect the different networks.

Advantages of IP Subnetting

• Reduced network traffic: Subnetting restricts traffic to the local network, reducing network congestion.
• Improved performance: Less traffic across routers leads to faster network operations.
• Simplified management: Smaller networks are easier to manage and troubleshoot.
• Facilitated spanning of large geographical distances: Connecting multiple smaller networks using WAN links, despite their cost and slower speed, can improve efficiency.

How to Create Subnets

• Subnets are created by borrowing bits from the host portion of an IP address and using them to define the subnet address.
• Borrowing bits for subnets results in fewer host bits, which means fewer hosts per subnet but more subnets in total.
• Carefully determining current and future needs is crucial.

Steps to Create Subnets

• Determine the number of network IDs (one for each subnet and wide area network connection).
• Determine the number of host IDs per subnet (one for each TCP/IP host and router interface).
• Create a single subnet mask for the entire network.
• Generate a unique subnet ID for each physical segment.
• Establish a host ID range for each subnet.

Subnet Masks

• Subnet masks are 32-bit values enabling IP packet recipients to differentiate network and host portions of an IP address.
• Every network device must have an assigned subnet mask (or uses the default from its IP address's class).

Classless Inter-Domain Routing (CIDR)

• ISPs use CIDR to allocate IP addresses to customers.
• CIDR notation follows the format IP_address/prefix_length (e.g., 192.168.10.32/28).
• /prefix_length indicates the number of bits in the subnet mask.
• The maximum subnet mask can only have a /30 because a minimum of two bits must remain for host bits.

Subnetting Class C Addresses

• Class C addresses have 8 bits for hosts, which may be borrowed for subnets.
• Subnets are based on borrowing bits sequentially; no bits can be skipped.
• Examples demonstrate resulting subnets for varied borrowings.

Subnetting a Class C Address (Fast Way)

• Five points to consider for Class C subnetting include: the number of subnets generated, the valid hosts per subnet, valid subnets, broadcast addresses per subnet, and valid hosts per subnet.

Subnetting Practice Examples (Class C)

• Specific examples of class C subnets, such as 192.168.10.0/25, 255.255.255.224 (/27), and 255.255.255.248 (/29), are provided.

Subnetting Class B Addresses

• Class B subnetting operates similarly to Class C, utilizing the third octet as a starting point.
• The same subnet numbers from the fourth octet in Class C should be used for Class B's third octet, with additions of zeros and 255s for network and broadcast parts of fourth octet, respectively.

Subnetting Practice Examples (Class B)

• Examples of Class B subnets include 255.255.128.0/17, 255.255.192.0/18, and 255.255.240.0/20.

Subnetting Class A Addresses

• Subnetting Class A is like subnetting Class B and C, but it starts at the second octet.
• Subnets are constructed through adding zeros.
• Broadcast addresses are derived by adding 255 in the third and fourth octets.

Subnetting Practice Examples (Class A)

• Examples include 255.255.0.0/16, 255.255.240.0/20, and 255.255.255.192/26.