IPv4 Addressing and Subnetting

Learning objectives

• Explain the purpose and scope of IPv4 Addressing and Subnetting.
• Identify important protocols, roles, fields, and terminology.
• Apply the concept to a practical network scenario.
• Use IOS XE commands to verify operational behavior.

1. Core concepts

IPv4 addresses are 32 bits. A prefix identifies network bits; /24 means 24 network bits and 8 host bits. The network address has host bits zero; directed broadcast has host bits one. A traditional /24 has 256 total and 254 usable host addresses.

2. How it works

Calculate a subnet by converting prefix to mask, finding the first non-255 mask octet, and calculating block size = 256 − mask value. Subnet boundaries are multiples of that block size. VLSM uses different prefix lengths; allocate largest subnets first and avoid overlap.

Visual walkthrough

3. Worked example

192.168.50.139/26 uses 255.255.255.192 and block size 64. Boundaries: 0, 64, 128, 192. The address is in 128–191: network .128, broadcast .191, usable .129–.190. Private ranges are 10/8, 172.16/12, and 192.168/16.

IOS XE commands and verification

Syntax and feature availability can vary by device family and software release. Confirm platform support before applying configuration.

show ip interface brief
show ip route connected
show ip arp
ping <same-subnet-host>

Common mistakes and troubleshooting

• Check physical and interface state before changing higher-layer settings.
• Verify both ends agree on addressing, VLAN, encapsulation, and protocol parameters.
• Use operational show commands; configured text alone does not prove a feature is working.
• Change one variable at a time and verify the result.

Knowledge check

Choose one answer per question. Submit to see why the correct choice is right and why every other option is wrong. These are original practice questions, not Cisco exam questions.