APPENDIX Subnetting and CIDR addresses INFORMATION IN THIS CHAPTER: · Netmask Basics NETMASK BASICS A netmask is a binary mask that is applied to an IP address in order to determine whether two IP addresses fall into the same subnet. It works by doing a binary AND of the IP address with the netmask to get the network address. If two hosts are in the same network, they are considered to be on the same subnet. To see how this works, let's take an IP address of 192.168.1.5 with a Classless Inter-Domain Routing (CIDR) mask of /24. The CIDR value is the number of bits that have been set in the