In the "old days" it was quite easy to register port numbers, and in fact I have registered a few myself that I still use for similar but not the same purposes (459, 1535, 1536). However, it appears to be not as simple anymore and looking at protocols that are in much more widespread use than AXUDP it appears to be not common anymore to register ports used only by some proprietary protocol at IANA (there are way, way more protocols in use than those with IANA-registered port numbers). Note that at the time I registered the above 3, IANA would not take suggestions for the numbers to register. I claimed different numbers that were unregistered, but they gave me those instead. Asking for port 93 to be registered is unlikely to succeed, 10093 may be possible. Registered port numbers are useful mainly for open protocols that are widely implemented and that accept unsolicited incoming connections. So everyone knows what port you have your wellknown services listening on. There is not much that can go wrong when using a port number without registering it, especially when the receiving application accepts data only from a pre-configured peer. The port numbers used essentially don't matter in that case, the only thing you need to make sure is that you don't have another session with that same peer that would want to use the same port number. (e.g. it would not be wise to use port 5198/5199 as these are used by Echolink, another port usage that is not registered at IANA and is in much more widespread use than AXUDP) Rob