Windows 10 as a router: NAT incoming NIC 1 traffic out via NIC 2

Question

I have a Windows 10 LTSB PC that I am trying to treat as a server (Running IIS and SQL) and a router, but the router side is giving me issues.
I have 1 Ethernet based NIC (192.168.1.180 no gateway) and 1 cell modem based NIC (100.100.7.31 gateway: 100.100.7.1).
My goal is to route all 100.100.X.X (255.255.0.0) to the cell modem so my device(s) connected to the ethernet NIC can communicate with the 100.100.X.X devices.

I currently get ping time out errors when pinging 100.100.X.X from my ethernet device, but I can ping the ethernet and modem NICs. In addition, my server can ping the 100.100.X.X devices and it can ping my ethernet devices, so it is only "ethernet -> server -> 100.100.X.X device" that doesn't work. My routing table is as follows:

===========================================================================
Interface List
 14...b4 9d 9f 5a 5f 48 ......Generic Mobile Broadband Adapter
 16...74 fe 48 21 b0 52 ......Realtek PCIe GBE Family Controller
  2...00 0b ab d8 69 90 ......Intel(R) I210 Gigabit Network Connection
  1...........................Software Loopback Interface 1
  9...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter #2
  7...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter #3
===========================================================================
IPv4 Route Table
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0      100.100.7.1     100.100.7.31      2
      100.100.7.0  255.255.255.192         On-link      100.100.7.31    257
     100.100.7.31  255.255.255.255         On-link      100.100.7.31    257
     100.100.7.63  255.255.255.255         On-link      100.100.7.31    257
        127.0.0.0        255.0.0.0         On-link         127.0.0.1    331
        127.0.0.1  255.255.255.255         On-link         127.0.0.1    331
  127.255.255.255  255.255.255.255         On-link         127.0.0.1    331
      192.168.1.0    255.255.255.0         On-link     192.168.1.180     11
    192.168.1.255  255.255.255.255         On-link     192.168.1.180    266
        224.0.0.0        240.0.0.0         On-link         127.0.0.1    331
        224.0.0.0        240.0.0.0         On-link     192.168.1.180    266
        224.0.0.0        240.0.0.0         On-link      100.100.7.31    257
  255.255.255.255  255.255.255.255         On-link         127.0.0.1    331
  255.255.255.255  255.255.255.255         On-link     192.168.1.180    266
  255.255.255.255  255.255.255.255         On-link      100.100.7.31    257
===========================================================================
Persistent Routes:
  Network Address          Netmask  Gateway Address  Metric
          0.0.0.0          0.0.0.0      100.100.7.1       1
===========================================================================

From my understanding, when I ping 100.100.X.X from my ethernet connected device, the server will not find a specific route for it, so it will use the default route of 0.0.0.0 and send the traffic to 100.100.7.1.
However, when I ping from my ethernet device, I do not get any replies. What am I doing wrong?

UPDATED THOUGHT AS A TYPED THIS:
Is this the flaw in my logic?: The server will route ALL 100.100.X.X traffic to the cell modem, including replies from 100.100.X.X devices, which causes a loop?
I send a ping to a 100.100.X.X device from my ethernet device, then the server routes the ping to 100.100.7.1, then gets a reply from 100.100.X.X, then routes that reply back through the 100.100.X.X route to 100.100.7.1 resulting in an infinite loop, causing the timeout (Explains why I don't receive net/host not found errors)

Other info:

The server has IP Routing (via regedit) turned on, and is reported as: IP Routing Enabled. . . . . . . . : Yes via ipconfig /all.
My ethernet device can successfully ping the cell adapter and ethernet adapter on the server (100.100.7.31 and 192.168.1.180 respectively)
My ethernet device does not receive any 'host not found' or 'net not found' errors when pinging

Pathping result when pinging a 100.100.X.X device from my ethernet device:

C:\>pathping 100.100.X.X
Tracing route to 100.100.X.X over a maximum of 30 hops
0  DESKTOP-BFB4MID [192.168.1.5]
  1  DESKTOP-UGFIN0H [192.168.1.180]
  2     *        *        *
Computing statistics for 25 seconds...
        Source to Here   This Node/Link

Hop  RTT    Lost/Sent = Pct  Lost/Sent = Pct  Address
  0                                           DESKTOP-BFB4MID [192.168.1.5]
                                0/ 100 =  0%   |
  1    0ms     0/ 100 =  0%     0/ 100 =  0%  DESKTOP-UGFIN0H [192.168.1.180]
Trace complete.

Ben Personick · Answer 1 · 2017-10-05T20:36:11.820

Follow these steps:

Plug laptop to Server on 192.168.1.x/24 network, Server IP .180 Laptop .5
Open the RRAS MMC (Start, control panel, admin tools, Routing and Remote Access)
Expand IPv4, right-click General, and then click New Routing Protocol.
In Routing protocols, click NAT, and then click OK.
Right-click NAT, and then click New Interface.
Select the interface that connects to the public Internet (Cell Modem 100.100.7.31), and then click OK.
Select both Public interface connected to the Internet and Enable NAT on this interface, and then click OK.
Restart the RRAS Service.

This should allow you to communicate as expected.

:)

I think this is an issue of not understanding some basic networking constraints.

I believe you are saying you have.

An internal network that is 100.100.x.x

--- Are these devices local and on a switch?  are you using any vlans?

A Cell Modem which is on the network 100.100.7.1
```
--- Plugged into a Switch?
```

A NIC on the server assigned IP 100.100.7.31

--- Plugged into the same switch and VLAN?

Another local network of 192.168.1.180

--- Guessing this is a LAN behind your router at home

I suspect you are just assigning servers IPs in the 100.100.x.x range without actually owning that address space (It is a public address space, not a private range, and must be purchased)

I also suspect that you assigned them all on a Layer 2 switch and subnetted down your cell modem to be the actual rage you have purchased from the provider.

So, I believe what you are intending to do is something like this:

Ditch the 100.100.x.x network and use say a 10.10.x.x/16 network for your servers

--- (Unless they are live on the internet on those 100.100.x.x/16 IP addresses and you want to reach them through the internet)

Setup a VLAN on the switch for each of the networks you want to route through the Windows 10 host.

--- IE the 100.100.7.x/26 network to the Cell modem, the 10.10.x.x/16 Network for the servers, and the 192.168.1/24 network for your VMs.

On the Windows 10 NIC create VLAN interfaces for each of these Networks.
In the RRAS Setup on your Windows 10 System configure it to use these vlan interfaces with appropriate network settings
Your default W on your Windows 10 system remains the same.
Your servers and other equipment on your 10.10.x.x/16 and 192.168.1.x/24 networks either change to the local IP of your Windows 10 machine on each of these networks or have a route added to them to reach appropriate networks through that path.
Your Cell modem is added a route to the 10.10.x.x/16 network and the 192.168.1.x/24 the network through the Ip of the windows 10 host on that network.

Clear?

Windows 10 as a router: NAT incoming NIC 1 traffic out via NIC 2

IPv4 Route Table

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