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Advanced Networking for Mactintosh Professionals


User Guide


IPNetRouter Guide to AirPort


  1. Introduction to AirPort and IPNetRouter
  2. Determining the Best Mac-based Wireless IP Solution
  3. Apple's Hardware Base Station Solution
  4. Base Station versus Computer-to-Computer mode
  5. Improving IPNetRouter and AirPort Compatibility
  6. Using IPNetRouter's FBA with AirportAdditional Important AirPort and Wireless Info

Introduction to AirPort and IPNetRouter

IPNetRouter can be used to expand the capabilities of a wireless network using a Mac as an Internet router or NAT gateway beyond the Airport hardware and software provided by Apple. Once Airport is verified to be working without IPNetRouter, you can just treat the Airport card as if it was an Ethernet interface for purposes of IP configuration for Internet sharing or routing for purpose of IPNetRouter configuration.

AirPort terminology. Apple's hardware and software base stations are sometimes referred to as "Access Points". For purposes of brevity, the abbreviation "HBS" is used for the hardware base station (aka hardware access point). Pay careful attention to the use of "Software Base Station" software, "Base Station mode", the AirPort card itself, and the HBS in the rest of this guide. The differences between the various components of wireless networking can be important when you attempt to configure IPNetRouter with AirPort hardware.


Determining the Best Mac-based Wireless Routing Solution

When you install Apple's software that comes with an Airport card, it includes a limited version of IPNetRouter that Apple licensed from us. The main reason you might need IPNetRouter for your wireless network is that Apple's own Base Station solutions are not adequate on their own. If all you want to do is to share a single Internet IP address among several wireless Macs then Apple's AirPort solutions may be all you need. Some of the things to consider are the number of subnets you will require, Appletalk capabilities for printing on your network, future capabilities, what interface you wish to perform NAT through, and many others.

IPNetRouter and AirPort Feature Table

Features IPNetRouter Apple Hardware Base Station Update (HBS) Apple Software Base Station release 1.3
More than one subnet on a single interface Yes No No
Requires Mac be on for routing/sharing? Yes No Yes
PPP over Ethernet (PPPoE) DSL Support Yes 1.3 or later with the 2.79 firmware update Yes
Supports more than one NAT Interface at a time? Yes, including the AirPort interface Ethernet or PPP only Not the AirPort interface and not more than one
NAPT with ICMP Yes No Yes
PPTP Support Yes No Yes
Route to other than Ethernet and AirPort Yes No No
Requires Mac with AirPort card Yes No Yes
DHCP servering on more than one interface Yes No Wireless only
Exposed Host (DMZ) Yes No Yes
Transparent Bridging Mode No Yes No
Computer-to-Computer mode support Yes No No
Cost $89+requires AirPort card $299 Included with AirPort card ($99)
We provide technical support Yes No No


Here are some specific reasons IPNetRouter might be a better wireless solution then Apple's software:

  • You wish to use a single or dual ethernet LAN with your AirPort gateway in addition to having a wireless component. AirPort 1.3 supports seperate wireless and Ethernet IP subnets simultaneously if you have a PPP dialup. Apple's software is limited in the address range supported and cannot use DHCP server services on the Ethernet portion of the LAN. IPNetRouter does not have these limitation and can be deployed as a full router between any ethernet or other physical interfaces that have the appropriate drivers. For example, TokenRing, Firewire, MacIP, etc.
  • Its cheaper overall for initial hardware cost then using a HBS. $99/AirPort card plus $89 for an IPNetRouter license. Since IPNetRouter permits two, three or more interfaces, you can use it to route/share between all IP multihoming compatible data link providers on a particular Mac. The HBS is limited to just one ethernet and one wireless LAN component.
  • IPNetRouter supports having the AirPort wireless interface be the one through which NAT takes place. Apple's user interfaces do not support IP Masquerading on the wireless interface.
  • You need other complex IP routing, filtering, and port mapping capabilities using the wireless Interface. As an example, IPNetRouter supports multiple sublans on single physical interfaces, including AirPort. Thus, using our software, you could have two seperate sublans sharing the same AirPort wireless link simultaneously.
  • Computer-to-Computer mode can be used with IPNetRouter. Apple's software requires Base Station mode to do Internet sharing. This has possible performance benefits.
  • You have a "PPPoE" style connection over a DSL modem. If you are not sure what type of DSL connection you have or will be getting, contact your local DSL provider to determine whether they require "PPP over Ethernet" to connect to their highspeed services. Many DSL providers require this for their cheapest high-speed accounts. Apple's AirPort 1.3 or later software supports some PPPoE implementations. Contact Apple for more info about PPPoE AirPort compatibility.
  • We can provide support for IPNetRouter configuration in conjunction with AirPort or other wireless solutions.


Apple's Hardware Base Station Solution

The AirPort Hardware Base Station is running a version of KarlBridge, which was developed by Doug Karl at Ohio State <>. Our routing configurator software is not part of this implementation. Apple's AirPort HBS is, however, a perfectly good wireless networking solution in many situations that might include IPNetRouter. Here are some points to consider about the HBS.

  • Transparent Bridging Mode(TBM) support. Apple's HBS can do Appletalk bridging because it does ethernet to wireless network bridging of all ethernet packets. (Although Appletalk and IP appear to be 100% supported in this mode, there may be other limitations with TBM--contact Apple to determine what is or is not supported by this mode.) IPNetRouter and Apple Software Base Station do not currently support Appletalk bridging/routing, although do support Appletalk as outlined in the IPNR FAQ. The HBS is better if you want to use Appletalk based printers and other Appletalk services across your wireless network.
  • Unlike the SBS and IPNR solutions, you don't interrupt routing to other wireless Macs if your gateway Mac is turned off. The HBS takes up very little power and, if power is maintained, should not have the potential for network disruption that restarting a Mac gateway might. However, if you are planning on keeping at least one machine continuously connected to the Interenet anyway…
  • Its $299. IPNR plus an AirPort card are less than $200.
  • Fortunately or unfortunately, purchasing the HBS means you are purchasing hardware that performs only one function. IPNetRouter can be used to route over all sorts of different transports, not just 10mb Ethernet and AirPort wireless. You are limited to that functionality for the life of the HBS.
  • IPNetRouter and the SBS-FBA support Trace Route (NAT with ICMP translation), can work with PPTP, and have various other implementation differences. As outlined elsewhere in this chapter, they have the potential to offer higher performance and more flexibility then the HBS.

Deciding on wireless networking solutions can be difficult sometimes. We are happy to field any questions on whether IPNetRouter may or may not be appropriate for your network. If you submit an IPNetRouter related AirPort question using our browser based support form we will be happy to respond. We should mention though that we are not the support solution for Apple's own AirPort software and hardware. If you are looking for AirPort support that does not involve the configuration of our IPNetRouter software, consult the AirPort documentation or contact Apple.


Base Station versus Computer-to-Computer mode

[Peter] Apple's Hardware Access Point (aka HBS) operates in Base Station mode only, whereas the AirPort software in combination with IPNetRouter can set the radio to either Base Station, or Computer-to-Computer mode (802.11 "ad-hoc" mode).

Base Station mode is similar to a cellular network and provides relaying and power saving features. The Base Station can buffer traffic for low power clients allowing them to periodically turn on their radio and ask the base station for any traffic that may be waiting. By switching on the radio only long enough to receive any waiting traffic, clients can save precious battery power by not operating the radio all the time.

In Computer-to-Computer (ad-hoc) mode, the radio listens for incoming traffic all the time. Computer-to-Computer mode is intended for setting up ad-hoc limited range LANs when no base station (or cellular network of base stations) is available. As a side effect, it may offer better network performance, but consumes more power. [Tim[ We recommend you use Computer-to-Computer mode with IPNetRouter whenever possible, thus avoiding arbitrary interruptions to your wireless network caused by the waking up and going to sleep of AirPort cards. Further, this reduces the chance of generating base station mode configuration files that give IPNetRouter conflicting instructions.

By setting the AirPort Software to use Computer-to-Computer mode along with IPNetRouter, it is possible to connect remote Ethernet LANs via wireless networking. AirPort wireless is just another data link provider logically equivalent to Ethernet.

Since Apple has not published the commands to switch the radio between Base Station and Computer-to-Computer mode, the only way to select Base Station mode is to use the AirPort Setup Utility (and then optionally modify the configuration or switch over to running the commercial version of IPNetRouter).


Improving IPNetRouter and AirPort Compatibility

Apple's Software Base Station (SBS) uses a licensed version of IPNetRouter supplied as a Faceless Background Application (FBA). This is important to remember when configuring IPNetRouter because this is mainly where potential conflicts arise. The following instructions apply to IPNetRouter 1.4.7 or later and AirPort 1.2 or later. We strongly recommend that you install/update to AirPort 1.2 or later to minimize conflicts between AirPort and IPNetRouter.

Installing the AirPort software may remove IPNetRouter's OTModl$Proxy extension and replace it with a possibly older version named "AirPort AP Support". Also note that Apple usually updates Open Transport itself with AirPort updates. Be sure to reinstall IPNetRouter, IPNetMonitor, IPNetsentry and/or any other third party networking software (like PPPoE client software) after installing a software update of any Apple AirPort software.

[Tim] In order to futher minimize any conflicts between the AirPort and IPNR I recommend that you use IPNetRouter only in Computer-to-Computer mode unless you have a good grasp of how AirPort works. It avoids the complications that can occur if your AirPort cards fall asleep or you accidently attempt to enable software base station mode with our software installed. I use this method on my own home office network quite effectively. Before I did this I had all sorts of problems!

Before installing IPNetRouter or while IPNetRouter is not running on the gateway Mac:

  1. Set Computer to Computer mode on the gateway Mac for AirPort.
  2. Verify that Appletalk works between the gateway and another wireless Mac using Filesharing. If it doesn't, don't proceed further until you can get this to work without IPNetRouter before proceeding.
  3. Open the AirPort Apple menu item
  4. Using the Software base station button, verify that your gateway machine is not in software base station mode. If it is running, turn this off and then close the "AirPort" window.
  5. Next, open the Extensions Manager control panel.
  6. Disable the "AirPort AP" and "AirPort AP Support" files. (These are the equivalent of the IPNetRouter FBA and "OTmodl$proxy" extensions. Disabling these extensions does not prevent AirPort from working but will prevent potential conflicts with certain files created when Software Base Station mode is configured on the IPNetRouter gateway machine; the files involved are explained elsewhere in the AirPort section of the Guide.)
  7. If the "AirPort AP Configuration" file is present in your system's Preferences folder, remove it (do not delete it if you might want to switch back to a software base station configuration you've used successfully in the past--always a good rule!).
  8. Reboot the gateway machine.
  9. Begin configuring IPNetRouter as you normally would for an Ethernet interface. See elsewhere in the IPNetRouter Guide for typical ethernet configurations.


Using IPNetRouter's FBA with AirPort

([Peter] The AirPort software Internet access point is a limited version of Sustainable Softworks Faceless Background App (FBA) and is configured using the AirPort Setup Utility. Turning on the Software Base Station feature writes out an IPNetRouter configuration file named "AirPort AP Configuration" in your Preferences Folder, and then sends an Apple Event to launch AirPort AP. Any changes you make to the Software Base Station writes out a new "AirPort AP Configuration" file. To use IPNetRouter to extend your AirPort configuration, you have two choices:

  1. Quit the AirPort AP FBA and launch the UI version of IPNetRouter to modify your IP network configuration directly.
  2. Modify AirPort AP to use a different configuration file that you specify (STR# resource 131 Option Settings, "ConfigFileName=AirPort AP Configuration"). [Note this technique is for registered IPNetRouter users who wish to integrate their use of IPNR with AirPort. Proceed at your own risk since the AirPort Setup Utility could produce unexpected results.]
  3. Use our FBA instead of Apple's. In this case, disable the AirPort AP files in your system's Extensions and Preferences folder.

To verify whether your AirPort AP configuration succeeded, you can examine the "AirPort AP.log" file in your Preferences Folder.


Additional Important AirPort and Wireless Info

Apple has updated AirPort Software and hardware firmware (for the HBS) several times since they were first released in 1999. Apple has also issued numerous technotes on some of the limitations and other idiosycracies of AirPort hardware and software performance and configuration since its introduction. To see all the technotes with regard to AirPort, use Apple's search engine. See also the IPNetRouter Troubleshooting section of our web site.

If you are looking for information about wireless LAN solutions other than Airport, a good place to start is our web based nettalk archives search engine.

Disclaimer: The information above is from existing published sources or otherwise readily available.