[Icecast] Nicecast (Mac) to Icecast/Icecast2

[DJ]

Dear group,

I have a problem configuring my NiceCast to work with my IceCast 
server.  Perhaps one of you can tell me how to solve the described issue 
I currently have.

Situation is as follows:
I run two gateways in my private network: (a) 10.10.10.100 and (b) 
10.10.10.200. My webserver is running on (c) 10.10.10.30 on which I have 
my internet radio station running. Port from and to (c) redirected to 
8000 for .m3u

I use Sam4 on a notebook (10.10.10.71) for streaming to (c). So far no 
problems.
Now I have an iMac on which I installed Nicecast (NC). From iTunes I 
want let Nicecast stream to my web server (c) like I do with my notebook 
now.
The problem I face is that I can't contact with NC to my webserver (c). 
Instead I can have it stream audio to (b) only. The problem is that I 
don't use that gateway to redirect to my sites but only (a).

Can someone hint me to the right direction to solve this issue?

thanks,
DJ