Different applications that run on the Internet use different port numbers.  For instance, the file transfer protocol (FTP) uses the port number 21.  The default  port number for the DVR is 80.  The IV-110 & IV-400 can be changed to also work on port 1080 and 2080.  If a router is used to connect a network to the Internet  make sure that there is not a firewall blocking traffic on the port you have set for your DVR.   Some Internet Service Providers also block traffic on certain ports requiring you to make a formal request to allow traffic on the desired port number or requiring a change to a different port on the DVR. On the IV-110 & IV-400 DVRs the port setting is found under Setup/Communications/Net IP.