forward requests by IP

[michal krajcirovic]

Hello,
trying to resolve some relatively simple problem. We have a webserver, 
it works NGINX. All the requirements that come with either sent from 
this site, or (as have the flv and mp4) to send to another server and 
send it from this second server
To use this simple rule in nginx.conf:

if (!-e $request_filename) {
rewrite ^(.*)flv$ http://second-server.cz$1flv;
rewrite ^(.*)mp4$ http://second-server.cz$1mp4;
}

New but need to be directed only to the requirements of this from some 
IP ranges (which is about 5000) and everything outside these ranges are 
odbavovalo directly from this server.
(the local node in the Czech Republic where the link is cheap providers 
from one datacenter, and external flow is cheap from the second 
datacenter).

Is there a simple solution to this problem?

Thanks a lot.