[CentOS] What on Centos is wiping out my eth0 IP address every 5 minutes?

[Rock]

On Tue, 23 Jul 2013 23:10:44 +0000, Rock wrote:

> I didn't want to complicate things, but whenever I use the GUI from right
> clicking on the four bars, the same thing happens (eth0 disconnects after 
> a few minutes):

Maybe I was editing it wrongly.

How does this look?
 http://i43.tinypic.com/n3lsnk.png

The question is what to make the "gateway" since the GUI insists on having
a gateway.

In my case, I'm plugging in a Ubiquiti Nanobridge M2 radio/router, which 
is configured, by default, on 192.168.1.20. 

So, I set the eth0 of the laptop to anything on that same subnet, e.g., 
192.168.1.100; but I don't know what to set the Network Manager "gateway"
to.

Q: Should I set the NM gateway to the IP address of the radio/router?

Note: The desired connection is:

a) Laptop sitting 300 feet from the house 
b) It's ok if the wireless wlan0 NIC is manually turned off 
c) The wired eth0 NIC is set to the subnet of the radio (e.g., 192.168.1.100)
d) I don't know *what* to set the eth0 gateway to (192.168.1.20?)

Then, a CAT5 cable is connected from the laptop RJ45 eth0 port to 
the one and only RJ45 port on the Ubiquiti Nanobridge M2 radio.

At that point, I would ping the radio (at 192.168.1.20) over that eth0 wire, 
and then connect over that same eth0 wire with Firefox to http://192.168.1.20 
(the default login = ubnt, and the default password = ubnt). 

Once logged into the radio GUI, I can set it up to connect to my home 
broadband router access point (or to a local Starbucks five miles down 
the road, for that matter).

QUESTION:
Given that the Network Manager is insisting on me giving it a "gateway", 
what would you suggest I set the "gateway" to in the Network Manager?

Note: I realize this may no longer be a Centos question...