Xnest -query just opens black window
 

In Centos 6.5, I'm trying
In Cygwin (Windows XP) on the same LAN, I can use
That Cygwin command opens a window with a login prompt and lets me login to xyz (another system on this LAN)

That Xnest command gives me a black window with a title bar.

I thought that Xnest command in Centos was supposed to do the same thing as that Xwin command in cygwin. Both should use XDMCP and XDMCP is enabled in system xyz.

The target system (xyz) is RHEL 6.5. I have ordinary user access to that system (not root).

My system is dual boot (Windows XP and Centos 6.5). It has the same hostname and the same IP address when booted as Windows as when booted as Centos (so xyz isn't differentiating by hostname or IP). I have root access on that system.

What should I try and/or what logs should I check to diagnose why this doesn't work? I can get things done by root on the target system with a couple days turn around by making IT requests. So if any steps require root on xyz, I'd like to have such steps exactly right before trying them.