This describes how to subnet a Class C address between two Netopia Routers and the ISP.
When setting up IP routing with a Class A Address, or even multiple Class C Addresses, subnetting is fairly straightforward. Subnetting a single Class C address between two networks, however, is vastly more complex. This Technical Note describes the general procedures for subnetting a single Class C network between two Netopia routers so that each can have Internet access.
Below is a list of hardware and firmware loads that this Technical Note is based upon:
| Hardware | Firmware/Version | Installed Options |
| Any Netopia router | 3.1.3 or later | None |
Below is a diagram of a simple network configuration. The ISP is providing a Class C address to the customer site, and both networks A and B want to gain Internet access through this address. Netopia B connects to Netopia A and is provided Internet access through Routers A and B.
The IP Addresses and routing configurations for the devices shown in the diagram are outlined below. In addition, each individual field and its meaning are described.
The 'IP Address' and 'Subnet Mask' fields define the IP Address and Subnet Mask of the device's Ethernet connection to the network while the 'Remote IP' and 'Remote Sub' fields describe the IP Address and Subnet mask of the remote router. This information is entered in the Connection Profile of the Netopia router.
The 'Gateway' field describes the router or workstation's default gateway or, where they will send their packets if the appropriate route is not known. The 'Static Route' field, which is only shown on Router B, tells Router B what path to take to get to the network defined by Netopia B. Finally, the 'Usable IP Address' field shows the range of IP Addresses available to the hosts of that network.
Please note that the IP Addresses given in this Tech Note are for example purposes only. Do not use these same addresses when configuring your network.
Below are the IP addresses and other information for the routers and workstations shown in the diagram.
IP Address: 10.0.0.1
Subnet Mask: 255.255.255.0
IP Address: 192.168.1.1
Subnet Mask: 255.255.255.128
Remote IP: 10.0.0.1
Remote Sub: 255.255.255.0
Gateway: 10.0.0.1
Static Route: 192.168.1.128 [network] 255.255.255.128 [mask] 192.168.1.2 [via router]
Usable IP Addresses available to Customer Site A: 192.168.1.1 --> 192.168.1.126
IP Address: 192.168.1.2
Subnet Mask: 255.255.255.128
Remote IP: 192.168.1.129
Remote Sub: 255.255.255.128
Gateway: 192.168.1.1
Usable IP Addresses available to Customer Site A: 192.168.1.1 --> 192.168.1.126
IP Address: 192.168.1.3
Subnet Mask: 255.255.255.128
Gateway: 192.168.1.1
IP Address: 192.168.1.129
Subnet Mask: 255.255.255.128
Remote IP: 192.168.1.2
Remote Sub: 255.255.255.128
Gateway: 192.168.1.2
Usable IP Addresses available to Customer Site B: 192.168.1.129 --> 192.168.1.254
IP Address: 192.168.1.130
Subnet Mask: 255.255.255.128
Gateway: 192.168.1.129
With this configuration, both Customer Site A and B can gain Internet access through Routers A and B, with no reconfiguration of the ISP's equipment. The most important item in this whole configuration is the Static Route defined on Router B. This tells Router B what path to take to get to the network defined by Netopia B. Without this information, Customer Site B will be able to access Customer Site A, but not the Internet.
If on Router B a Static Route is not able to be defined, RIP could be enabled to serve the same purpose. To use RIP instead of a Static Route, enable Transmit RIP on Netopia A and Transmit and Receive RIP on Router B. This will allow the route from Customer Site B to propagate on Router B and Customer Site A.
Subnetting a single Class C Address between two networks is quite complex and this Technical Note describes the general procedures for subnetting a single Class C Address between two Netopia routers so that each can have Internet access.