most cams have dynamic dns already set up, if you find that from the settings it should stay the same forever (that's the whole point of it).
could be something like "549846516.vipcam.org" or "8008.no-ip.org"
if you are having trouble finding it through the webui, you can check for one by going to camera/get_params.cgi
looks like this:
var ddns_service=17;
var ddns_user='user';
var ddns_pwd='password';
var ddns_host='8008.no-ip.org';
var ddns_proxy_svr='';
var ddns_proxy_port=0;