Thank you Scott for saving me the time to type the correct response.
Additionally the subnet mask 255.255.255.0, a class "C" mask provides for allocation of any address between .1 and .254 to ANY device. A "gateway" is a device within your physical subnet which is aware of and can forward your IP address to a device NOT seen by you local subnet, typically but not always a router.
Therefor if your subnet is 192.168.1.xxx
And the mask is 255.255.255.0
You can then "see" any address on the 192.168.1.xxx subnet .1 through .254
If you set the default gateway to 192.168.1.1, then ANY time your 192.168.1.xxx device CAN NOT find the address within your subnet that you have asked for 192.168.1.1 is looked at to see if that address has an answer, or knows where to send your packet of data. You may not always like the answer you receive as traffic can also be blocked using a set of complex rules in which case you may have discovered a "firewall".
So if your PC or board is addressed;
192.168.1.10
255.255.255.0
GW=192.168.1.1
and your router is addressed as 192.168.1.1, where does the board look if it can't find 192.168.10.55 ?
It looks at the router and asks the router if it knows where 192.168.10.55 is located. Your router then looks at the networks it is aware of to see if it can resolve the address. If not you will eventually (500ms) receive the dreaded address unknown reply.
That is why you can use anything inside the house up to the router (outside world). From that point subnets are licensed and why your provider issues the IP address for your home router. They own the subnet addressing scheme you attach to.
Keep your network simple, live long, and prosper.
