Chapter 8 – Sections & Objectives

8.0 Introduction
8.1 Subnetting an IPv4 Network
- Explain how subnetting segments a network to enable better communication.
- Explain how to calculate IPv4 subnets for a /24 prefix.
- Explain how to calculate IPv4 subnets for a /16 and /8 prefix.
- Given a set of requirements for subnetting, implement an IPv4 addressing scheme.
- Explain how to create a flexible addressing scheme using variable length subnet masking (VLSM).
8.2 Addressing Schemes
- Implement a VLSM addressing scheme.
8.3 Design Considerations for IPv6
- Explain how to implement IPv6 address assignments in a business network.
8.4 Summary

8.1 Network Layer Protocols

Broadcast Domains
- Each router interface connects a broadcast domain.
- Broadcasts are only propagated within its broadcast domain.
Problems with Large Broadcast Domains
- Slow network operations due to the significant amount of broadcast traffic.
- Slow device operations because a device must accept and process each broadcast packet.
Reasons for Subnetting
- Solution: reduce the size of the network to create smaller broadcast domains.
- Because each broadcast domain connects to a different router interface, each domain needs its own network address space.
- The process of breaking an address range into smaller address spaces is called subnetting.
- Network administrators can group devices into subnets that are determined by location, organizational unit or device type.

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Creating Subnets with a /16 Prefix
- A subnet mask of /16 applied to 172.16.32.0, creates a network with 65534 hosts.
- A subnet mask of /18 applied to 172.16.32.0, creates 4 networks with 16382 hosts in each network.
- A subnet mask of /22 applied to 172.16.32.0, creates 64 networks with 1022 hosts in each network.
Creating 100 Subnets with a /16 Prefix
- A subnet mask of /23 applied to 172.16.32.0, creates 128 networks with 510 hosts in each network
Calculating the Hosts
- Use 2h-2 to calculate the number of hosts.
- h is the number allocated to the host portion of the address.
Creating 1000 Subnets with a /8 Prefix
- A subnet mask of /18 applied to 20.0.0.0, creates 1024 networks with 16382 hosts in each network

Subnetting Based on Host Requirements
- Two considerations when planning subnets:
  - The number of host addresses required for each network.
  - The number of individual subnets needed.
Subnetting Based on Network Requirements
- Administrators may be asked to subnet an IP range to accommodate a specific number of networks.
- Think of a company with 7 departments where each department must have its own subnetwork.
- The number of hosts per subnet, while secondary, is also important.
Network Requirement Example
- Assume the range 200.42.98.0/24 was given to the administrator.
- 7 subnets must be created.
- Each department will have no more than 29 hosts.
- A subnet mask of /27 applied to 200.42.98.0/24, creates 8 networks with 30 hosts in each network.

Traditional Subnetting Wastes Addresses
- Subnetting based on classes is not very flexible.
- Results in wasted addresses.
Variable Length Subnet Masks
- By varying the mask, an administrator has more control.
- Less waste.
Basic VLSM
- A subnet mask of /30 applied to 200.42.98.0, creates a network with 2 hosts in each network.
- The network 200.42.98.0/30 would be a perfect match for a serial link.
VLSM in Practice
- Consider two routers connected by a Serial link:
- RouterA would be 200.42.98.1/30 and RouterB would be 200.42.98.2/30.
- 200.42.98.0/30 is the network address and 200.42.98.3/30 is the broadcast address.

Network Address Planning
- Planning requires decisions on each subnet in terms of size, the number of hosts per subnet and how host addresses will be assigned.
Planning to Address the Network
- The Primary Planning Considerations are:
  - Prevent Duplication of Addresses
  - Monitor Security and Performance
  - Provide and Control Access
Assigning Addresses to Devices
- Different devices needs may also impact the addressing scheme.
- Common devices are:
  – End user devices, servers, printers, network devices and gateways

The IPv6 Global Unicast Address
- The IPv6 global unicast address normally consists of a /48 global routing prefix, a 16 bit subnet ID, and a 64 bit interface ID.
Subnetting Using Subnet ID
- The subnet ID provides plenty subnets and host support in one subnet.
- The subnet ID alone allows for creating up to 65,536 /64 subnets.
IPv6 Subnet Allocation
- Address waste is not a concern in IPv6.
- Administrators can concentrate on designing a logical scheme to address the network

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Implement an IPv4 addressing scheme to enable end-to-end connectivity in a small to medium-sized business network.
Given a set of requirements, implement a VLSM addressing scheme to provide connectivity to end users in a small to medium-sized network.
Explain design considerations for implementing IPv6 in a business network.