Understanding why some IPs don't have a mask address
<p>I am given a list of IPs, some of them have a netmask, other no.
I got the idea of how to create a mask but i'm not understanding why there are cases where an IP doesn't have a mask.</p>
<p>Like the following:</p>
<ul>
<li>121.34.56.64–121.34.56.128 &gt; Don't have mask</li>
<li>128.131.9.0–128.131.9.192  &gt; Don't have mask</li>
<li>93.20.10.0–93.20.11.0      &gt; Don't have mask</li>
</ul>
<p>While the following actually have mask address:</p>
<ul>
<li>67.56.34.64-67.56.34.79 &gt; Prefix notation: 67.56.34.64/28 | Address/Mask: 67.56.34.64/255.255.255.240 and so on.</li>
</ul>
<p>For example if I look at the third one of the addresses without mask i do the following:</p>
<blockquote>
<p>93.20.10.0–93.20.11.0</p>
<p>93.20. 0000 101|0 . 0000 0000<br />
93.20. 0000 101|1 . 0000 0000</p>
<p>NetMask: 255.255.254.0, that is not correct.</p>
</blockquote>
<p>Can somebody explain me why and how to understand when a mask exists?</p>