IP Addressing and Subnetting

IP Addressing and Subnetting

• Network devices leverage IP addresses and subnets for identifying communication sources and destinations, as well as for managing network addresses.
• IP addresses are composed of two elements: a network identifier (network ID) and a host identifier (host ID).
• The network ID specifies a network area where a device is located and the host ID labels a particular device within that network segment.
• Most business networks continue to operate on IP version 4 (IPv4) addresses, approximately 4.3 billion unique variations are available.
• The newer IP version 6 (IPv6) standard provides more addresses and other benefits.
• Computers utilize IPv4 addresses as 32-bit binary strings, but humans generally use a dotted decimal address for easier writing and understanding.
• Binary string 11000000.00000000.00000010.00000010 converts to the IP address 192.0.2.2.
• The associated subnet mask of the converted IP address converts from 11111111.11111111.11111111.11111100 to 255.255.255.252.
• Subnet masks are important in distinguishing the network ID from the host ID within an IP address.
• Routers, computers, and troubleshooters rely on IP addresses and subnet masks to efficiently manage network traffic and guarantee information arrives at the correct destination.

IP Address Fundamentals

• Network devices typically possess the following three identifiers: Physical address (MAC address), Logical address (IP address), and Hostname.
• A workstation is identified by a hostname, IP address, and MAC address.
• In IPv4 networks, each host has a unique IP address, enabling nodes to exchange information.
• Data is segmented into packets with source and destination IP addresses, like postal service mail containing destination and return addresses.
• Network segmentation allows administrators to manage network traffic effectively, improve security, and control traffic flow to improve performance.
• Network segments are called subnetworks or subnets, each having a unique identifier within the broader network ID.

IP Address Ranges

• Public Internet systems consume most of the available IPv4 addresses, but private networks can reserve address ranges for internal use.

Private IPv4 Address Ranges

• The list below defines private IPV4 address ranges and their default subnet masks
• Class A: Range 10.0.0.0, Default subnet mask 255.0.0.0, Larger networks with many hosts
• Class B: Range 172.16.0.0, Default subnet mask 255.255.0.0, Medium networks with a moderate number of hosts.
• Class C: Range 192.168.0.0, Default subnet mask 255.255.255.0, Smaller networks with fewer hosts.

Subnet vs. Subnet Mask

• "Subnet" and "subnet mask" are often confused, but they describe separate networking elements.
• Subnets serve as isolated network segments created by an administrator.
• The reasons network administrators typically create subnets are security, isolating traffic for privacy and performance, and managing traffic to reduce network congestion.
• Security subnets are designed to prevent unauthorized traffic from traversing network, example Finance department restricted to a single subnet, finance network communications from moving across the entire network.
• Performance subnets mitigate competition for network access on congested networks.
• Subnet masks are used by devices to determine the network ID and host ID within an IP address, as well as the network area to which they are connected.

IP Address Classes

• IPv4 addresses are divided into five categories that are used to categorize the number of subnets versus the number of hosts per subnet
• Class A: First octet - 1 to 126, Number of subnets - 126, Number of hosts - Approximately 16.7 million, Description - Many hosts per network
• Class B: First octet - 128 to 191, Number of subnets - 16,384, Number of hosts - 65,536, Description - Many hosts per network
• Class C: First octet - 192 to 223, Number of subnets - Approximately 2.1 million, Number of hosts - 254, Description - Many networks with fewer hosts per network
• Class D: First octet - 224 to 239, Number of subnets - n/a, Number of hosts - n/a, Description - Multicasting.
• Class E: First octet - 240 to 254, Number of subnets - n/a, Number of hosts - n/a, Description - Experimental.
• Class D addresses support multicasting for transmitting data to many devices.
• Class E addresses are only used for experimentation / research, rather than networking.
• This design introduces inefficiencies in address utilization. Class B networks permit 65,000 host IDs, but Class C networks only permit 254 host IDs.

Classless Inter-Domain Routing

• Classless addressing enables administrators to define network IDs at any preferred point and enables for efficient use of the available addresses.
• A Classless Inter-Domain Routing (CIDR) notation is placed at the end of a subnet mask, specifying a number of bits in the subnet mask.
• Using Classless Inter-Domain Routing (CIDR) notation we can add more IP addresses using a different class.

Examples of Subnet Masks with Their Corresponding CIDR notations

• /19 - 255.255.224.0; 8,192 hosts per subnet.
• /20 - 255.255.240.0; 4,096 hosts per subnet.
• /21 - 255.255.248.0; 2,048 hosts per subnet.
• /22 - 255.255.252.0; 1,024 hosts per subnet.
• /23 - 255.255.254.0; 512 hosts per subnet

Troubleshoot IP Addresses and Subnet Masks

• Network administrators face troubleshooting common IP address issues: misconfiguration and inability to communicate with network service.
• The first network troubleshooting step is to verify these settings, including the subnet mask.
• Network administrators should update subnet masks with valid settings if they're incorrect.
• Command to display IP Address settings on three popular OSes
• Linux, Command - ip addr
• Windows, Command - ipconfig
• macOS, Command - ifconfig

Troubleshooting cont.

• Most workstations, tablets, smartphones and devices receive their IP addresses via a Dynamic Host Configuration Protocol (DHCP) server.
• The DHCP server contains many configurations, and a properly configured server does not make any typographical errors.
• Automatic Private IP Addressing (APIPA) is assigned if a DHCP server is unable to receive an IP address configuration.
• An APIPA address start with 169.254, but the configuration will not communicate correctly with other networks.

In Summary

• IP addresses and subnet masks form a fundamental requirement of network operation, ensuring each node has a unique IP address with associated identifiers.
• Subnet masks help define the network and host portions of an IP address
• Network administrators create subnets to isolate traffic for security and performance.
• Most business networks rely on IPv4, using Classes A, B and C
• Netowrk professionals need to understand troubleshooting tools such as ipconfig, ip addr, ifconfig and ping