Module 9: IPv4 and Network Segmentation

IPv4 Unicast, Broadcast, and Multicast

The IPv4 protocol supports three types of transmission modes: unicast, broadcast, and multicast. Each mode defines how data is sent across the network and to which devices the data is directed.

1. Unicast transmission refers to a one-to-one communication where a device sends a message to only one other device. The packet has a unique destination IP address, indicating a single recipient. The source IP address will also be a unicast address, meaning it originates from a single device. IPv4 unicast host addresses range from 1.1.1.1 to 223.255.255.255.

2. Broadcast transmission involves one-to-all communication. A broadcast message is sent to all devices within a broadcast domain. The destination IP address for a broadcast packet contains all ones (1s) in the host portion, with 32 one (1) bits. Broadcasts may be either:

   • Directed Broadcast: Sent to all hosts on a specific network.
   • Limited Broadcast: Sent to the special address 255.255.255.255. Routers do not forward broadcast packets by default, limiting their reach to the local network.

3. Multicast transmission is one-to-many communication. A host sends a single packet to a specific group of devices, rather than all devices on the network. This reduces unnecessary traffic. IPv4 multicast addresses are reserved in the range 224.0.0.0 to 239.255.255.255. Hosts that wish to receive multicast traffic must subscribe to a multicast group and will process packets sent to the group’s multicast address.

Types of IPv4 Addresses

IPv4 addresses are categorized into different types, each serving a specific purpose in network communication.

1. Public IPv4 addresses are globally unique and routed across the internet. They are assigned by Internet Service Providers (ISPs) and are necessary for devices to communicate over the internet.

2. Private IPv4 addresses are used for internal networking within organizations or home networks. These addresses are not routable on the public internet. The private address ranges are:

   • 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 Private addresses must be translated to public addresses using Network Address Translation (NAT) before being sent over the internet.

3. Loopback addresses (127.0.0.0/8) are used by a device to communicate with itself. The most commonly used loopback address is 127.0.0.1. These addresses are primarily used for testing and troubleshooting.

4. Link-local addresses (169.254.0.0/16) are used when a device cannot obtain an IP address from a DHCP server. These addresses are automatically assigned by the device to allow local communication on the network.

IPv4 Classful Addressing

In the early days of IPv4, addressing was done based on classful addressing, which defined address ranges based on the size of the network. The key classes were:

• Class A: From 0.0.0.0/8 to 127.0.0.0/8, designed for large networks with over 16 million hosts.
• Class B: From 128.0.0.0/16 to 191.255.0.0/16, designed for medium-sized networks with up to 65,000 hosts.
• Class C: From 192.0.0.0/24 to 223.255.255.0/24, designed for small networks with a maximum of 254 hosts.
• Class D: Reserved for multicast addresses (224.0.0.0 to 239.0.0.0).
• Class E: Reserved for experimental purposes (240.0.0.0 to 255.0.0.0).

Network Segmentation

Network segmentation involves dividing a large network into smaller, more manageable subnets. This helps to control traffic, reduce congestion, and improve security. It addresses issues with large broadcast domains where excessive broadcasts can negatively impact network performance.

Subnetting is the process used to create smaller networks (subnets) within a larger network by borrowing bits from the host portion of the IP address. This is done by adjusting the subnet mask, which specifies which portion of the IP address is used for the network and which part is for hosts. The benefits of subnetting include:

• Reducing Broadcast Traffic: Smaller broadcast domains mean fewer devices are affected by broadcasts.
• Improved Security: Subnets can be isolated, and access between subnets can be controlled.
• Better Network Performance: Less congestion and better control of traffic flow.

A switch propagates broadcasts across a network and sends them to all devices, except the one from which the broadcast was received. In a large network, too many broadcasts can slow down the network. By creating smaller subnets through subnetting, these broadcasts are confined to the subnet, improving the overall network performance.

Network administrators also use subnetting to apply security policies. For example, they can restrict communication between subnets based on security requirements or organizational needs. Additionally, smaller subnets reduce the number of devices affected by network misconfigurations, hardware failures, or malicious activities.