hello Ubuntu Community

I'm having a problem I installed a New Ubuntu Server 12.04 with 2 network cards, One with a static public address and one with a private address.

#public
iface eth0 inet static
address xxx.xxx.xxx.xxx
netmask 255.255.255.248
gateway xxx.xxx.xxx.xxx
dns-nameservers xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx

#intern
iface eth1 inet static
address 192.168.10.9
netmask 255.255.255.0
gateway 192.168.10.4
dns-nameservers 192.168.3.4
dns-search example.com


I have internet, access with the Public IP.
The problem is that I cant do ping to another network (ex. 192.168.15.1) but I can to my computer or inside the 192.168.10.0 network, either can't do ping from another network to my server.

I really don't know the whats the problem, maybe someone can help Pls.

Thank you