https://support.tools/tags/ip/Recent content in IP on Support ToolsHugoen-USTue, 27 Oct 2026 00:00:00 +0000https://support.tools/subnet-mask-cheat-sheet/Sat, 19 Oct 2024 14:00:00 -0500https://support.tools/subnet-mask-cheat-sheet/<h2 id="what-is-a-subnet-mask">What is a subnet mask?</h2> <p>A subnet mask is a 32-bit number that splits an IPv4 address into two parts: the <strong>network</strong> part, which every device on the same subnet shares, and the <strong>host</strong> part, which identifies one device on that subnet. Bits set to 1 in the mask mark the network part; bits set to 0 mark the host part.</p> <p>Take <code>192.168.1.10</code> with the mask <code>255.255.255.0</code>:</p> <div class="code-block" data-copy-label="Copy text code, block 1"> <div class="code-block-header" data-pagefind-ignore><span class="code-block-lang">text</span></div> <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-text" data-lang="text"><span class="line"><span class="cl">IP address 192.168.1.10 11000000.10101000.00000001.00001010 </span></span><span class="line"><span class="cl">Subnet mask 255.255.255.0 11111111.11111111.11111111.00000000 </span></span><span class="line"><span class="cl">Network 192.168.1.0 (IP AND mask) </span></span><span class="line"><span class="cl">Broadcast 192.168.1.255 (host bits all 1) </span></span><span class="line"><span class="cl">Usable hosts 192.168.1.1 to 192.168.1.254</span></span></code></pre></div> </div> <p>The first 24 bits of the mask are 1, so that mask is written <code>/24</code> in CIDR notation, and <code>192.168.1.10/24</code> means the same thing as <code>192.168.1.10</code> with mask <code>255.255.255.0</code>. A device compares the network part of a destination address with its own: if they match, it delivers the packet directly on the local network; if not, it sends the packet to its default gateway.</p>