Figure 1 shows a server running a DNS server on port 53 and a RADIUS server on port 1812.  The figure has two clients accessing the server.  Client 1 is sending a DNS request from source port 49152 to destination port 53.  Client 2 is sending a RADIUS request from source port 51152 to destination port 1812.  This demonstrates how port numbers are used to differentiate between multiple services running on one server. Figure 2 highlights the use of the well-known ports for the services. Figure 3 highlights the use of random port numbers as the source ports. Figure 4 highlights the response from the server to each of the two requests and the fact that the server uses the source port from the request packet as the destination. Figure 5 highlights the new destination port.