Internet, Networking, & Security Home Networking 94 94 people found this article helpful 255.255.255.0 Subnet Mask for IP Networks Master the secrets of the subnet mask 255.255.255.0 by Bradley Mitchell Writer An MIT graduate who brings years of technical experience to articles on SEO, computers, and wireless networking. our editorial process LinkedIn Bradley Mitchell Updated on March 23, 2020 reviewed by Jessica Kormos Lifewire Tech Review Board Member Jessica Kormos is a writer and editor with 15 years' experience writing articles, copy, and UX content for Tecca.com, Rosenfeld Media, and many others. our review board Article reviewed on Apr 19, 2020 Jessica Kormos Home Networking ISP The Wireless Connection Routers & Firewalls Network Hubs Broadband Ethernet Installing & Upgrading Wi-Fi & Wireless Tweet Share Email The subnet mask 255.255.255.0 address is the most common subnet mask used on computers connected to Internet Protocol (IPv4) networks. Besides its use on home network routers, you might also encounter this mask on network professional certification exams such as the CCNA. 255.255.255.0 and Subnetting Lifewire / Joshua Seong Subnets act as virtual fences, splitting a block of IP addresses into smaller units. This practice relieves network congestion and allows for granular access across subnets. A subnet mask identifies individual subnets. Traditional subnets worked with classful networks that partitioned the IP addresses into one of five classes (Class A/B/C/D/E) according to the value of the IP address number. The subnet mask 255.255.255.0 converts to a 32-bit binary value: 11111111 11111111 11111111 00000000 The 0 digits of this mask span the IP range of the subnet—8 bits or up to 256 addresses in this case. A larger number of smaller-sized subnetworks can also be defined by modifying the mask as shown in the table below. Classful Subnets Based on the 255.255.255 Mask Prefix Mask Subnetworks Nodes/Subnet 255.255.255.0 1 254 255.255.255.128 2 126 255.255.255.192 4 62 255.255.255.224 8 30 255.255.255.240 16 14 255.255.255.248 32 6 255.255.255.252 64 2 An incorrectly configured subnet mask (also called netmask) causes some types of network connection failures. Subnets and CIDR In the traditional classful scheme, many unused IP addresses were wasted because internet service providers and large corporations reserved address blocks that could not be shared. Much of the internet subsequently converted to classless IP networking to support flexible allocation policies and cope with the surge in demand for IPv4 internet addresses in the 1990s. Classless networks convert the traditional subnet representation to a shorthand notation based on the number of 1 digits in the mask. Classless Inter-Domain Routing shorthand writes an IP address and its associated network mask in the form: xxx.xxx.xxx.xxx/n Here, n represents a number between 1 and 31 that is the number of 1 bits in the mask. CIDR supports classless IP addressing and associates network masks with IP network numbers independent of their traditional class. Routers that support CIDR recognize these networks as individual routes, even though they may represent an aggregation of several traditional subnets. Network Classes The InterNIC organization that administers internet domain names divides IP addresses into classes. The most common of these are classes A, B, and C. Class C networks use a default subnet mask of 255.255.255.0. Using 255.255.255.0 as an IP Address Although expressed in the form of an IP address number, network devices use 255.255.255.0 as a mask and not as a working IP address. Attempting to use this number (or any IP number that starts with 255) as a device address causes the IP network connection to fail due to the definition of number ranges on IP networks. More from Lifewire IP Tutorial: Subnet Mask and Subnetting IP: Classes, Broadcast, and Multicast CIDR: Classless Inter-Domain Routing 192.168.0.100 IP Address for Local Networks What It Means When You See the 0.0.0.0 IP Address Definitions and Examples of Wireless Technology How Is the 192.168.0.0 IP Address Used? MAC Addresses With Formatting Examples Linux Tips for Troubleshooting Windows File and Printer Sharing What Are TCP/IP Router (Routing) Tables? How to Change the IP Address on Your iPhone Why the 10.0.0.2 IP Address Is Used What is an IP Packet? IP Address Forward and Reverse DNS Lookup What Is a NETGEAR Router's Default IP Address?