National VPN

Hi everybody,
I have done a national VPN with cisco router using site-to-site GRE
tunneling option.
All works fine i can ping any computer of any vpn but i have a little
problem.
I need to show you how is the netwok first:

primary net secondary net
192.168.1.0/24 192.168.34.0/24

cisco871 (VPN) cisco871(VPN)
192.168.1.50 192.168.34.254

default gw default gw
192.168.1.254 192.168.34.254

Example PC A Example PC B
192.168.1.10 192.168.34.10



As you can see the problem is that in the first network I have a default gw
different from the cisco871 vpn.
So if I set default gw on PC A as *.254, then PC B is unalbe to ping PC A,
while PC A is always able to ping PC B.
But if I set gw of PC A as *.50 then all works fine.

I use a linux box as firewall as 192.168.1.254 as default gw, I also put a
route table to route any packets coming from 192.168.34.0/24 network
throught 192.168.1.72 (cisco 871 VPN).
But that seems not to work :/ I mean if i ping from PC B any computer in the
first network none reply :/

Please help me!

thanks for any advice

Agus