ubuntu 12.04, using NetworkManager package to manage 2 eth ports.

1. At 1st we have only 1 port,
eth0, static ip 10.38.150.214,

root@utilite-ubuntu-desktop:/opt/ultra# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 10.50.183.254 0.0.0.0 UG 0 0 0 eth0
10.38.144.0 0.0.0.0 255.255.248.0 U 1 0 0 eth0
10.50.183.254 0.0.0.0 255.255.255.255 UH 0 0 0 eth0


i ping the windows 7 pc (host 10.50.176.234) from linux, good.
ping linux eth0 from windows 7, good.

2. now i plugin cable for eth1, this is using dhcp,
ip is 10.50.176.212, routing table is updated automatically,

root@utilite-ubuntu-desktop:/opt/ultra# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 10.50.183.254 0.0.0.0 UG 0 0 0 eth1
10.38.144.0 0.0.0.0 255.255.248.0 U 1 0 0 eth0
10.50.176.0 0.0.0.0 255.255.248.0 U 1 0 0 eth1
10.50.183.254 0.0.0.0 255.255.255.255 UH 0 0 0 eth0

From windows, i can ping eth1 (10.50.176.212), but not eth0 anymore,

Any suggestions pls ?
Thanks very much !

did you enabled forwarding by setting net.ipv4.ip_forward = 1

run this command sysctl -a | grep net.ipv4.ip_forward and see its valuse if it is zero change it to 1

What are you trying to do?
Can you make a scetch of the network layout?