[Mark McLeod]

There is no gateway in the network, so you can leave that blank.
Supplying a fictitious IP address for a device that doesn't exist (e.g., .4) won't harm things, but it also won't matter.

When this FRC control system was first developed for the 2009 season we were issued a router used at the driver station plus a separate robot bridge. That router was assigned the address 10.te.am.4. However, that router wasn't a gateway either.

A gateway typically takes you to a WAN or Internet, not to someplace else on the same LAN.
A gateway is a transition point from one type of network to another.
Since none of our robot network traffic leaves our LAN, a gateway is never used or even looked for. (and by IP convention private IP addresses like 10.xx.yy.zz are not allowed through gateways anyway)
In general, the gateway field is only required when you have a more complex network where network traffic must hop across several different types of networks or get out through an Internet Service Provider.