Hello all. We're trying to determine which ports are open on a specialized piece of hardware in our lab. We have Red Hat 5.9 as the host to scan it and have tried the following nmap commands:

nmap -v -sU -p U:1-65535 <ip address>

This doesn't have the desired effect and, from reading how this actually works under the hood, since the OS considers this a ping sweep (kind of), it responds with, "Not gonna do it", yet it will tell you how many ports were found opened. I believe they mentioned the OS as having a built-in failsafe to thwart would-be attacks in this manner.

What's interesting about this is that if you shorten the range of ports to, say, 100 or so, apparently the OS doesn't mind and will actually tell you the port(s) opened and the protocol associated with it.

So, my question is, how does one determine all opened UDP ports on a host without the OS getting in the way?

For me it works. The exact message you get after this command is really "Not gonna do it"? It should display a reason why command was unsuccessful. Are you running this command with root privilages?

Yes, run as root (or you'd get the message that it fails immediately because it requires root, of course).

When I do the entire port range, it tells me there were x number of ports opened, but it doesn't give me the rundown I'm expecting to see that includes the typical port and protocol columns.

Are you saying you're seeing this?

Yes, I get this result:Maybe there are nmap version differences.