You can have processes listen on 0 - which means all available IPv4 IPs (available to that machine).<p>And since you can have processes listen on 0, it means you can equally curl 0; just like you could with 127.0.0.1. Here&#x27;s an example from my IRC server (the only process I run on 0):<p><pre><code>    $ curl https:&#x2F;&#x2F;0:9997 -kis | head
    HTTP&#x2F;1.1 200 OK
    Date: Fri, 12 Feb 2016 07:49:24 GMT
    Server: ZNC - http:&#x2F;&#x2F;znc.in
    Content-Length: 1878
    Content-Type: text&#x2F;html
    Set-Cookie: 9997-SessionId=54245f15ba592bc691e09ac75e6778e6d4c33841fad71a8d6c56addc998e043f; path=&#x2F;;
    Connection: Close

    &lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot;?&gt;
    &lt;!DOCTYPE html PUBLIC &quot;-&#x2F;&#x2F;W3C&#x2F;&#x2F;DTD XHTML 1.1&#x2F;&#x2F;EN&quot; &quot;http:&#x2F;&#x2F;www.w3.org&#x2F;TR&#x2F;xhtml11&#x2F;DTD&#x2F;xhtml11.dtd&quot;&gt;
</code></pre>
(just in case someone queries, 0 is just another notation of 0.0.0.0)