Mind Wide Open CISCO. Cisco Networking Academy® Lab - Calculating IPv4 Subnets Objectives Part 1: Determine IPv4 Address Subnetting Part 2: Calculate IPv4 Address Subnetting Background / Scenario The ability to work with IPv4 subnets and determine network and host information based on a given IP address and subnet mask is critical to understanding how IPv4 networks operate. The first part is designed to reinforce how to compute network IP address information from a given IP address and subnet mask. When given an IP address and subnet mask, you will be able to determine other information about the subnet. Required Resources · 1 PC (Windows 7 or 8 with Internet access) · Optional: IPv4 address calculator Part 1: Determine IPv4 Address Subnetting In Part 1, you will determine the network and broadcast addresses, as well as the number of hosts, given an IPv4 address and subnet mask. REVIEW: To determine the network address, perform binary ANDing on the IPv4 address using the subnet mask provided. The result will be the network address. Hint: If the subnet mask has decimal value 255 in an octet, the result will ALWAYS be the original value of that octet. If the subnet mask has decimal value 0 in an octet, the result will ALWAYS be 0 for that octet. Example: IP Address 192.168.10.10 Subnet Mask 255.255.255.0 Result (Network) 192.168.10.0 Knowing this, you may only have to perform binary ANDing on an octet that does not have 255 or 0 in its subnet mask portion. Example: IP Address 172.30.239.145 Subnet Mask 255.255.192.0 Analyzing this example, you can see that you only have to perform binary ANDing on the third octet. The first two octets will result in 172.30 due to the subnet mask. The fourth octet will result in 0 due to the subnet mask. IP Address 172.30.239.145 Subnet Mask 255.255.192.0 Result (Network) 172.30 .?. 0 Perform binary ANDing on the third octet. @ 2020 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public.
Lab - Calculating IPv4 Subnets Decimal Binary 239 11101111 192 11000000 Result 192 11000000 Analyzing this example again produces the following result: IP Address 172.30.239.145 Subnet Mask 255.255.192.0 Result (Network) 172.30.192.0 Continuing with this example, determining the number of hosts per network can be calculated by analyzing the subnet mask. The subnet mask will be represented in dotted decimal format, such as 255.255.192.0, or in network prefix format, such as /18. An IPV4 address always has 32 bits. Subtracting the number of bits used for the network portion (as represented by the subnet mask) gives you the number of bits used for hosts. Using our example above, the subnet mask 255.255. 192.0 is equivalent to /18 in prefix notation. Subtracting 18 network bits from 32 bits results in 14 bits left for the host portion. From there, it is a simple calculation: 2(number of host bits) - 2 = Number of hosts 214 = 16,384 - 2 = 16,382 hosts Determine the network and broadcast addresses and number