I have a linux home router, with 3 nic's,
eth0: for internet
eth1: for the first local subnet
eth2: for the second local subnet

It runs nat from the 2 local cards to the internet, with :

echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

On slackware i had to add routes between the 2 local subnets manually if i wanted them to access each other.
Like this:
#/sbin/route add -net netmask gw metric 1
#/sbin/route add -net netmask gw metric 1

On ubuntu however this routing is on by default, and i don't want that at the moment. (second subnet is for a different apartment, i don't want them browsing my shares/network printer etc).

How do i turn this off?