I figured out the problem.  The gateway addresses need to be empty.  If you delete the entry and create a new one you can use an empty gateway address.  If you have an address in the field, including 0.0.0.0, you cannot save an empty gateway address.

On Tue, Oct 6, 2015 at 5:56 PM, linux guy <linuxguy123@gmail.com> wrote:

I need to connect a wifi device to my Linux computer. There is no router in between the two. Just my computer and the device. The device has a fixed IP, 192.168.0.10. It has its own Wifi interface built in  It isn't capable of connecting to a router.  It has a fixed IP address.

My home wifi network uses 192.168.1.x. It has a router. It works fine. My computer connects to it via its built in wifi interface.

I have added a USB wifi interface (dongle) to my computer to connect to the device. My computer displays the device properly in a network manager scan. So the device is available for connections.

Next I edit the connection for the device in network manager. The SSID is filled in from the scan. I select Ad-hoc mode. Band, Channel, etc. are all automatic.

Next I edit wifi security. The device is open security wise, so I select None.

Next I edit the IPV4 tab. Under connection method I select Manual.

The next fields are DNS server and Search Domains. In a point to point connection, there will be no DNS server. I leave the boxes blank.

Next up is adding the static IP address, netmask and gateway.

I set the address of my interface to be 192.168.0.123, because it was recommended by another user who connected with an Apple device. I set netmask to 255.255.255.0.

The next thing to set is the gateway address. Here is where I get confused.  What is a gateway in the context of a peer to peer connection ?  I try to leave it blank, but it won't let me.  So I put in 0.0.0.0.   I also tried the address of the interface (192.168.0.123) and the address of the device (192.168.0.10)

Then there is a route field.  I add a route for the ip address 192.168.0.10, using a netmask of 255.255.255.0 and again it asks for a gateway. I tried 0.0.0.0, the device address and the interface address.

I don't touch any of the IPV6 settings because the device doesn't support IPV6 addresses.

I save everything and connect to the device successfully.

I run "arp -a" and the device is found connected to the interface.  Yippee !

Pinging the device fails.  Destination Host Unreachable.

When I ping the device and watch in wireshark I see an ARP broadcast message "Who has 192.168.0.10 ? Tell 192.168.0.123". 192.168.0.123 is the static IP for the interface. And that is as far as the process gets.

When I watch the other interface and do a ping to a local device, I see the same ARP broadcast message, but also a reply message to it. 192.168.1.142 is at <device MAC> And then the process continues successfully.

So what am I missing in the setup of my adhoc connection such that the OS knows that a message sent to my device (192.168.0.10) gets routed through the USB wifi interface, ie the ARP broadcast message gets a reply ?

Thanks.