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Getting Started with IPNetRouter

General Setup Configurations and Examples

You Can Download similar instructions as a PDF
(recommended for configuration when not connected)

These pages provide instructions for using IPNetRouter to share a single Internet connection with other computers (Internet Sharing). The directions assume you have IPNetRouter 1.5 or later. Many of the instructions may apply to older versions of IPNetRouter and we are still updating information to reflect the newer 1.5 user interfaces and features.

Before getting into specific examples, here is a quick overview and some general instructions. First, IPNetRouter can configure your Mac to do:

  1. Internet Protocol (IP) Multihoming - the ability to use more than one IP interface via Ethernet, PPP, Airport wireless, etc at the same time.
  2. IP Forwarding - the ability to route IP traffic from one network interface to another.
  3. IP Masquerading - the ability to hide multiple IP hosts behind a single public IP address using Network Address Translations (NAT).

Taken together, these three features allow you to share a single connection to the Internet with an entire Local Area Network or Networks (LAN or LANs). For Internet sharing, one of your Macs will run IPNetRouter and become a "gateway" that provides Internet access to the rest of your LAN. The other machines on your LAN may be referred to as either "slaves" or "clients". Any IP standard compliant machine may be used as an IP client. Windows, Macintosh, Unix, and LPR printers may be IP clients. IPNetRouter need only be installed on the gateway Mac; installation of IPNetRouter on other machines on your private LAN is not required.

IPNetRouter can configure your Macintosh to perform other standard IP router functions as well and does not have to be used solely as an Internet gateway router. Additional features include a DHCP server and IP Filtering on each separate interface.

Since IPNetRouter depends on Open Transport and TCP/IP being present, there are two very important setup considerations for the machine running IPNetRouter:

1. When IPNetRouter is not running, you MUST UNCHECK "Load Only When Needed" in the TCP/IP Control Panel so that TCP/IP will remain loaded at all times (Edit > User Mode set Advanced mode, select Options...). If you are connecting via PPP, you must uncheck "Load Only When Needed" for both your Ethernet and PPP TCP/IP control panel configurations.

2. While IPNetRouter is running on your Mac, the Mac should NEVER go completely to sleep. You can configure your Energy Saver control panel so that the machine never sleeps. Dimming or turning off the screen is okay, harddrive spindown is not recommended.




The following examples cover the most common network configurations.

Basic Networking

General IPNetRouter Setup

Advanced Techniques


These directions may seem foreign if you are not familiar with IP networking. Here is some further background information to help you get started.


Internetworking 101

The Internet is actually a network of thousands of privately run networks using different equipment with only minimal coordination needed between them. This minimal coordination gives the Internet the ability to expand and evolve rapidly since almost anyone can add their network to the Internet. It can also lead to problems when some piece of equipment you know nothing about breaks down or coordination fails.

To manage this vast enterprise, the Internet is organized into hierarchical sections or domains.


Message processing computers called "Routers" or "Gateways" are used to connect individual networks together, with specialized Gateways used at exchange points where different carriers or service providers can exchange traffic between their respective networks.

In order to communicate with another computer on the Internet, your computer will normally go through four steps:

  1. Lookup the address of the host you wish to communicate with. Since people aren't very good at remembering lots of numbers (IP addresses), host computers on the Internet are usually identified by a name; a domain name. The domain name usually includes both the name of the individual host, and a hierarchy or list of names that describe the domain or part of the network where it resides. This is like calling directory service to find someone's telephone number. On the Internet, this type of directory service is called a Domain Name Service (DNS), and computers that handle these requests are called Name Servers.

  2. Determine if the IP address is local to this network, or if the message needs to be forwarded to another network. This is kind of like determining if you need to dial a country code plus the region or area code before dialing the rest of a phone number.

  3. If the IP address resolved by the Name Server is local to a network, the message is delivered directly.

  4. If the IP address is not local to this network, the message is sent to a router or gateway that can forward the message on to its destination. This process can be repeated through a dozen or more networks before the message is actually delivered.

Understanding these steps is helpful because it tells you what information every computer must have to access the Internet.

  1. A unique IP address that identifies the IP interface.
  2. A network mask used to divide the IP address into a network number and host number.
  3. The address of a Name Server used to translate domain names to their corresponding IP address.
  4. The address of a router or "Default-Gateway" to forward any packets that cannot be delivered directly.

The secret to efficient routing on the Internet is that IP addresses are carefully assigned based on where a computer is connected to the network. Just as the area code and exchange part of a phone number are used to identify where a call needs to be routed, the first part of an IP address serves the same purpose. If you move to a new calling area, you are assigned a phone number for that area. Similarly, when you connect to an ISP (Internet Service Provider), you are assigned an IP address for that part of the network.

To make configuring your computer easier and reduce the total number of IP addresses required, many ISPs will assign you a temporary (dynamic) IP address every time you connect to one of their access servers. You simply set your computer to get its IP address using a particular method (typically PPP, DHCP, or PPPoE) from the ISP's dynamic address server. A dynamic IP server may also assign your computer a network mask, router, and name server address information. Configuring an IP interface essentially means identifying what network connection the interface should use, and then filling in the required information described above. On a Mac, this information is generally entered or shown in the TCP/IP control panel.

Using Dynamic Host Configuration Protocol (DHCP) on your own LAN can be especially useful if you have many computers and/or frequently move a computer--like a portable--between two or more IP networks. IPNetRouter includes a DHCP server. You can optionally enable this server and configure clients on your LAN to get their IP address, router address, etc via DHCP. Using the DHCP Server may avoid the need to manually enter IP, mask, and router address on each computer on your LAN. To avoid conflicts with your ISP's network we strongly discourage the use of a DHCP server in single ethernet configurations for Internet sharing. More information on the DHCP server feature and DHCP is available elsewhere on our website and in the DHCP Server window help text of IPNetRouter.


All I want to do is share my Internet connection between two machines, why do I have to learn all this stuff?

IPNetRouter, using Open Transport, is the first low cost software that allows you to do this on a Macintosh . The program to make it simple hasn't been written yet. User interfaces for configuring IP will see more progress in the coming years, We hope to help you through the coming odyssey.

For more information on TCP/IP networking, may we suggest:

  • "Internetworking With TCP/IP, Volume 1", by Douglas E. Comer
  • "TCP/IP Illustrated, Volume 1" by W. Richard Stevens
  • "Troubleshooting TCP/IP: Analyzing the Protocols of the Internet" by Mark A. Miller

For more tutorial information on Macintosh and general Internet-workings on the web:

For searching for Internet standards documents on the web: