I have Ubuntu 10.04 installed on my desktop computer which has a device with a fixed address connected to a gigabit port which has a fixed address assigned to it. They happily communicate. Now I am trying to get the same application running on a ThinkPad T61 with the same device. I have Ubuntu 10.04.2 loaded on the T61. The ethernet port on the T61 communicates nicely with a router using DHCP. However, when I try assigning a fixed address the ethernet interface becomes inactive. I have tried editing the file /etc/network/interfaces to include appropriate information for having eth0 have a fixed address. That doesn't work. I am looking for some fresh ideas.