If the domain is &quot;loopback&quot;, then no address information is necessary -- the sending and receiving machines are one and the same.</DD>
<DT>
<STRONG>
Port</STRONG>
</DT><DD>This token identifies one side of a connection within one machine. Ports allow multiple data sockets to operate over one connection. Thus, connecting to &quot;geoworks.com&quot;, one might send mail messages using port 25 and file-transfer commands via port 21. Port numbers are either 16-bit or 32-bit, depending on the domain.</