Ubuntu

hello,
first of all i am new to unix so maybe my problem is very easy for many of you but is very important to me.

So the idea is that i want to use a ubuntu 10.4 machine as a router from eth0 to eth1.
but the traffic routing is nor working properly

i configured the 2 interfaces to be part of 2 subnets and then i tried to use iptables command.
sudo sysctl -w net.ipv4.ip_forward=1
iptables -A FORWARD -i eth0 -o eth1 -j ACCEPT
iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT

the result was
sudo iptables -L -n -v
Chain INPUT (policy ACCEPT 5493 packets, 4815K bytes)
pkts bytes target prot opt in out source destination

Chain FORWARD (policy ACCEPT 254 packets, 16979 bytes)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- eth0 eth1 0.0.0.0/0 0.0.0.0/0
1 60 ACCEPT all -- eth1 eth0 0.0.0.0/0 0.0.0.0/0

Chain OUTPUT (policy ACCEPT 5349 packets, 888K bytes)
pkts bytes target prot opt in out source destination

unfortunately there was no trafic between the interfaces an even i could ping eth1 and eth0 from the pc-s from the subnetworks i was unable to ping from one pc to the other

digging more i found that if i run
sudo iptable -t nat -A POSTROUTING -j MASQUERADE everithing works perfect

unfortunately i need the ipaddresses of the PC and the NAT here is not doing more wrong than good.

please give me some ideas why this hapens

i add here the result of the route command
destination Gateway Genmask Flags Metric Ref Use Iface
100.10.10.0 * 255.255.255.0 U 1 0 0 eth1
192.168.10.0 * 255.255.255.0 U 1 0 0 eth0
link-local * 255.255.0.0 U 1000 0 0 eth0
default 192.168.10.1 0.0.0.0 UG 0 0 0 eth0

What IP Address have you given to eth0 and eth1 respectively?
Are the LAN cables plugged into different physical networks?

thanks for your reply,

eth0 192.168.10.110 /24 gateway 192.168.10.1
eth1 100.10.10.2/24 gateway 192.168.10.110

eth0 is conected to a CISCO switch
eth1 is connected to a windows pc with the following config

IP 100.10.10.1
mask 255.255.255.0
gateway 192.168.10.110

switch == [(eth0) ---ubuntu ----(eth1)]==windows pc

yes there are 2 phisical interfaces and i used straight cable from the switch to the ubuntu pc and cross between ubuntu and windows pc

---------- Post updated 05-11-12 at 08:33 AM ---------- Previous update was 05-10-12 at 11:16 AM ----------

still no answer

digging through i found about routing. well i have now a big question : is't my problem one which is to be solved by altering the routing table and not by modifying the iptables? I ask this because iptables i think deals with firewalling and the firewall check if some trafic is to be allowed or not but it does't say how to route it. and if my hypotesis is true why when implementing masquerading everything worked great.
looking forward to hearing some opinion.