The short answer is that at least one device that is on both networks (probably the computer with two NICs) could be configured to route from one network to the other.
It is simpler to configure one larger network (such as would be created if you set the netmask to 255.255.0.0), so that is another option.
Routing makes sense if there are bandwidth limitations, or if you want to create a control / choke-point.
It looks like you want to set up routing. You have a few devices you care about, and a few interfaces:
- NAS - 10.0.1.50
- IP camera - 10.0.2.50?
- Two-NIC computer (router?) - (NIC#2:10.0.2.1, NIC#1:10.0.1.?)
- AirPort - 10.0.1.1?
You'll need to configure the two-NIC computer to route between its two interfaces. This depends on the OS, but shouldn't be a roadblock.
The IP camera can be configured (using DHCP) with NIC#2 of the router (10.0.2.1) as its default gateway, because that device sits between it and all other networks.
The NAS can be configured with the AirPort's IP as its default gateway, and the router's NIC#1 as its route to 10.0.2.0/24.
The router should probably be configured with the AirPort as its default gateway (it already knows about both directly connected networks, so it just needs to know how to get to the Internet / other networks)
You might configure the AirPort to route 10.0.2.0/24 traffic towards the router's NIC#1. That could save you configuring the NAS individually, and allow all devices on the 10.0.1.0/24 network to reach 10.0.2.0/24 without additional configuration. It may not work perfectly though; some equipment doesn't like to route out the same interface the packet came in. There is another solution to that, but it is more complex.
Specific to the UI displayed:
Revised Question: How do I set my routes via this GUI up so that I can
access the 10.0.2.x from the 10.0.1.x main network and vice versa?
- Destination: 10.0.2.0 (This is the IP portion of the destination network.)
- Netmask: 255.255.255.0 (This is the netmask portion of the destination network)
- Gateway: 10.0.1.? (The IP address of the device that routes to the destination network)
- Metric: (Shouldn't matter)
- Interface: (If you only have one active interface, choose that one. Otherwise, choose the interface that is closest to the gateway)
Rules to live by:
- A route consists of a network you are trying to reach, and a device on the same network you are on that will pass traffic towards that network you are trying to reach. (And sometimes a metric, but don't worry about that at this scale)
- A default gateway is a fallback route / route of last resort for packets that aren't headed towards a network with a defined route. Because of this, it doesn't need you to specify a network; just the IP address.
- A network can be expressed a variety of ways, including:
- 1.2.3.0/24 - The first available IP address in the network, followed by a / and then the number of leading (most significant) bits that are consistent for all IP addresses in the network.
- 1.2.3.0, netmask: 255.255.255.0 - The first available IP address in the network, followed by an IP address that has all bits set that are consistent for ip addresses in the network (e.g. /24 == 255.255.255.0, /16 == 255.255.0.0, /30 == 255.255.255.63)