I have to add a gateway to my net for experimental reasons.
Actually there are : a main-router that works as interface to the Internet,
and some hosts on my sub net.

        Internet-----MyRouter----MySubNet

NOw i need to configure one host of MYSubNet to act as a gatway for the
secondary subnet.
Both the 1SubNet and 2 SubNEt share the same ip-range.

     Internet-----MyRouter----MySubNet-----My2SubNet

All the sub.net have to be seen from the Internet so I'll need to add a
route to MainRouter in order to route the Secondary Subnet.
The problem is that i cannot change configuration of the mainroute,so i
wonder if is possible to configure the new gateway to do a sort of "proxy
arp" for my secondary Subnet.
But arp-tables are system-wide so if i change arp entry to cacth request on
PrimaryNet the 2subnet dont'works anymore.
Is possible to catch arp request only on a single subnet,without broke any
other subnet connected to the same host.?
thank you!