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Use a second ethernet card for internet sharing Network
This hint applies to sharing a high speed Internet connection, such as a cable modem, with other computers on your local Ethernet network. It's not necessary if you are sharing a high speed Internet connection with your PowerBooks on your Airport network instead of the Ethernet network. Internet Sharing allows all the other computers to access the Internet through your Mac. It turns your Mac into kind of a router.

Routers usually have two ethernet ports: One public port for connection to the outside world, and one private port for connection to the internal private network. This allows the router to protect any traffic in the internal private network so that it stays private. The problem is that most Macs have only one Ethernet port.

You can still do Internet sharing with your built in Ethernet port but the internal data has no protection. It can be risky if some data gets out. If you have any doubts, go to the Internet Sharing Control Panel and turn on "Share the Connection with other computers on Built-in Ethernet". You'll get this scary message:
In some cases (if you use a cable modem, for example) you might unintentionally affect the network settings of other ISP customers, and your ISP might disconnect you to prevent network disruption.
Yes. Your Mac's DHCP server (from Rendezvous) could set your neighbor's IP address to the incorrect number! Ouch! This can happen because cable modems make it as if you and your neighbors are all on the same LAN.

The solution is to add a PCI ethernet card to make a completely separate private internal network. I used a cheap spare Ethernet card from a PC that had a DEC Tulip chip on it, but any card that is supported by OS X will do. A USB Ethernet adapter will work too. It should give you the same results. My experience is that USB is a bit slower, more expensive, and a bit less reliable since it's easy to accidentally disconnect the cable. For those of you with iMacs, USB is your only option.

I installed the card. It was recognized by OS X without me even installing a driver. Now I could start Internet Sharing. Once started I got this nice message:
You are connected to the Internet over Built-in Ethernet. This connection will be shared with computers connected to Airport and PCI Ethernet Slot 3.
I connected the PCI Ethernet card and the other computers to a hub. To my amazement (I'm used to Windows), when I started up the other computers, it all just worked.

[Editor's note: I just love that last line!]
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Okay I'll bite...
Authored by: pizza_the_hut on Sep 11, '02 12:30:39PM

Which ethernet cards *are* supported under OS X? I've been looking for an offical list with this information for over a year. I've tried (pre-10.2, of course) several RealTek chipset NIC's with no luck at all.

-- I maybe slow, but I'll get there eventually. --

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RealTek driver for Jag.
Authored by: socoast on Sep 11, '02 02:18:24PM

I have a very cheap ($5) no-name PC NIC with a RealTek chip. I downloaded the RealTek driver for OSX and it works fine under Jaguar.
I got the URL from

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Okay I'll bite...
Authored by: Anonymous on Sep 11, '02 04:38:06PM

The D-Link DFE-530TX+ (note the plus) is easy to find, and works fine on my DP 800.
It has the Realtek chipset that works with OS X.
I found this card by searching the MacNN forum. --mk

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Ethernet cards in Jaguar
Authored by: BradMacPro on Sep 14, '02 12:13:09PM

Don't have a list but a Asante 690 card worked for me in Jaguar. Look for kext files for a suggestion of a list.

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Longshine LCS-8038 TX
Authored by: couzteau on Sep 29, '02 07:03:47PM

the Longshine LCS-8038 TX works fine after downloading the driver for RTL8139 (the chip) from

currently it's only beta, but it works fine.
it's only €20 (euros)

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OS X compatible network cards
Authored by: geraldo on Oct 11, '02 03:55:24PM

see at:

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I have a second ethernet AND Airport
Authored by: 47ronin on Sep 11, '02 01:57:32PM

At first I failed cause I bought some Netgear 10/100 card, so I did my homework and got a Farallon 10/100 which worked right out of the box in OSX. With Internet Sharing turned on, it automatically routes the 'Net through en1 (second ethernet) and en2 (Airport). Note that to make this work you need to set IPs for all interfaces.

In my case, on en1, I set it to, subnet, router, DNS set to my cable modem's DNS server. For Airport, I set it to, subnet, router, DNS set to my cable modem's DNS server.

Make sure you get a firewall up of course; I use a firewall.conf file that was originally generated by BrickHouse, but now I just use the StartupItem and customize the rules file myself. It works great.

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I have a second ethernet AND Airport
Authored by: xeroply on Sep 12, '02 12:10:34AM

I'm a bit confused. The original hint said that it worked just fine after turning on Internet Sharing. This post says that it requires all this particular networking setup.

So, assuming you're right -- how did you choose the IP addresses and subnet masks that you list? (Why is Airport set up with a private IP -, while Ethernet is set up with a public address - ??? Does this have something to do with NAT that AirPort does?) How would I figure out what IP to give a PCI ethernet interface?


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I have a second ethernet AND Airport
Authored by: paulio on Sep 12, '02 04:40:40PM

You don't have to setup any IP addresses. Set DHCP in System Preferences Network (for Built-in Ethernet). You probably have this already if you have a working cable modem or DSL. Then turn on Internet Sharing. The rest all just works.

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I have a second ethernet AND Airport
Authored by: inertiavvv on Feb 15, '03 12:20:42AM

I can't give you any reason as to why the airport base station is assigned a prefix 10.x.x.x ip address and why the other a 192.x.x.x address, but I am pretty sure that both are private IP address prefixes. Still, I am curious if there is a particular reason for assigning the different IP prefixes, or whether it is simply an arbitrary decision.

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USB Ethernet adapter - Where?
Authored by: jmacak on Sep 11, '02 07:21:56PM

The hint notes that "a USB Ethernet adapter will work too." I need one of these, but have not been able to find one that is supposed to Mac compatible. There are several available that claim Windoze compatibility, but not Macintosh.

Can anyone point me to an adapter that will definitely work through a Mac's USB port to give me Ethernet connectivity?


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Ethernet cards that work
Authored by: paulio on Sep 11, '02 07:54:31PM
The only ethernet card that I have had success with is the SMC Dual port EtherPower adapter. The board uses a DEC Tulip chipset, which is what is really important. Many boards used this chipset. This chipset is quite old so you I doubt that you can buy these new, but that's a good thing. You can get them cheap on eBay. Here is a partial list of cards that use the DEC Tulip chipset. I just did a quick Google search: Digital 21x4x Tulip PCI Ethernet cards SMC EtherPower 10 PCI(8432T/8432BT) SMC EtherPower 10/100 PCI(9332DST) DEC EtherWorks 100/10 PCI(DE500-XA) DEC EtherWorks 10 PCI(DE450) DEC QSILVER's, Znyx 312 etherarray Allied Telesis LA100PCI-T Danpex EN-9400, Cogent EM110 also from the RedHat website: LinkSys EtherPCI, Netgear FA310TX 10/100Mbps, Macronix MX98713 PMAC, Macronix MX98715 PMAC. Here is another listing of DEC Tulip cards. See the section on Supported Ethernet Cards:

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Ethernet cards that work
Authored by: paulio on Sep 12, '02 04:46:20PM

A quick check on shows that SMC EtherPower boards going for $10. Note that SMC EtherPower II boards are NOT the same - they do not have the DEC chipset so they probably won't work.

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What about PC Cards for Powerbooks?
Authored by: Tastannin on Sep 12, '02 02:32:02AM

I'm thinking of getting a cheap G3 series powerbook for use as a Firewall/Router (since it can be put out of the way easily, and has its own UPS, etc) and will want to run OS X on it. Which Ethernet PC Cards does Jaguar recognize?


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Multiple Ethernet Networks with a single Ethernet Card
Authored by: eduo on Sep 12, '02 06:48:40PM

I was thinking of sending this as a hint but I think it's either something well known or not of much interest.

In MacOSX it's very easy to use the same ethernet card for two separate networks. You can do it the hard way (using the terminal and ifconfig and manually routing around) or using the network preferences control panel, duplicating your network ethernet connection and putting different parameters in it. You can have as many as 255 different networks through the same ethernet cable and ethernet card. They all have different names so they are treated as separate by the firewall programs. I am currently running three different ethernet networks in my mac, plus the modem. I am routing between them all for five users who work for me but everyone else in the networks has to use the "official" routers for their respective areas. I am also doing a bit of routing, nat and firewalling through one of the ethernet networks and through the modem link, to skip on some of the networks' restrictions.


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IP networks are very different from Ethernet networks.
Authored by: paulio on Sep 13, '02 10:25:23PM

I know it might seem like being picky, but you have NOT created two Ethernet networks. You have created two IP networks. The two are very different things.

You are right. You can easily create two IP networks by typing in two IP addresses in the Network preferences. Even easier, you can turn on the setting, "Share the Connection with other computers on Built-in Ethernet" in the Sharing preferences. I used to do it that way myself.

The result will be that your mac will have one Ethernet card with two IP addresses. You will have two separate IP networks on the one Ethernet network. That's all ok.

You still have only one Ethernet network.

The dangers are with the lower level protocols that have no concept of IP address. A DHCP query is one of these. It can go to any machine on the Ethernet network regardless of IP address. Remember that a DHCP query is a query asking FOR an IP address. The machine is asking for an IP address because it does not yet have one.

With a cable modem, it is as if your neighbors are on your same Ethernet network. Their computers see every packet that your computer sends and vice versa, regardless of IP address. Note the random flickering on your cable modem. Those are their packets going your way.

Therefore, if either your Mac, your Airport base station, or some other device on your Ethernet network happen to have their DHCP server running, then that DHCP server can set your neighbor's IP addresses to the wrong number. That's a bad thing.

The solution is to have two Ethernet cards, creating two Ethernet networks, one for the public Internet, one for the private internal network.

For me, the question is: for all devices on my Ethernet network, do I know for SURE that there are no DHCP servers running? Do I even know for sure whether DHCP the only thing that I need to worry about? Well, I don't know, so I find it best to have two Ethernet cards. Why worry?

Besides, perfectly good used Ethernet cards cost $10 on eBay.

This kind of problem is not supposed to happen for DSL, but I also don't know for sure. Could it depend upon the service provider's implementation? Why worry?

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What about 10.2 Server?
Authored by: Anonymous on Sep 14, '02 11:22:48AM

Maybe it's just cuz I haven't read the entire 600+ page manual for OS X Server 10.2, but it is not this easy with X server. I have 10.2 server running on a B&W G3 tower with two working NICs and I cannot find out how to do routing between my external network and my private internal network. DHCP works fine on the internal network, but no external names resolve and even trying to pull up outside IP addys fails. How do I set-up the routing on X server?

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Internet Sharing
Authored by: pekk on Oct 01, '02 07:53:18PM

Please, I can't get this working. It seems that it is so easy that everybody forgets to give clear instructions.
OK. I have two ethernet cards working (Mac running OS X). One goes to the ADSL modem and the other to an ethernet hub where also is connected another Mac. So, what are the TCP/IP settings on the second card? (the card that goes to the ADSL is already ok) AND what are the TCP/IP settings in the Mac on the network? What differences would be if this Mac is running OS 9 or OS X? (currently switching between both in this Mac).
I've tried a lot of settings and no one seems to work. Please help!



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Internet Sharing
Authored by: cocomac on Oct 02, '02 09:55:27AM

I have and still use only a single CableModem connection and share it with 3 Macs (G4933,G4433,G3iBook500). Works perfect and not only I use a LOT of different settings and the best of it. is I do not use Private IPs (192.168.x.x-10.x.x.x-etc) I use complete Blocks of Numbers a do not even own.
EG:(X06.105.128.0/19)-(X00.8.0.0/16) (X=real#). But they are dead networks not active, meaning impossible for others not in your network to access to that IP but makes my HUB and Router more secure and responsive.
I will not tell how to do it here, but if you are tempted and at least know a bit about networks, I will be more than happy to explained it in a more private place.
The information is real and have been used for more than 2yrs.

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Authored by: bluehz on Oct 02, '02 04:54:35PM

How do you manipulate a firewall for two NIC cards (or 2 virtual IP's if using only one NIC). For example - what if you wanted one IP to have a certain set of parameters and the other IP to have completely different parameters?

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Configuration for 2nd network card
Authored by: paulio on Nov 21, '02 10:07:15PM
I keep getting qestions about this hint, so here is something that doesn't seem to be answered.
hi, Thanks for your explanation on how to internet share from OS X 10.2. I also have a Mac with 2 network cards. It receives internet signal from the cable modem on the built in very well. The second card is linked to an ethernet hub which in turn is lnked to 3 macs on OS X 10,2, two with cable and one with airport. My question is: What configuration do you use for the second network card and for the client computers network panel?
Hi Michael, I've found that the biggest problems with macs occur when I think that the solution is complicated, so I search for a complicated solution. The solution to this one is stupidly easy. I was amazed myself. The answer is no configuration. Don't do anything that could possibly configure the second network card. Don't setup NAT or do anything strange or unixy like that. Go to System Preferences | Sharing | Internet. It will tell you exactly what is happening: You are connected to the internet using built-in ethernet. This connection will be shared with computers connected to ethernet card in pci slot 2, or something like that. Click on the Start button. That's it. The only complication is that each time you restart, you will have to manually click this start button. Use this hint to make it automatic.

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Internet sharing Tips
Authored by: Anonymous on Nov 27, '02 11:59:53PM

Hi Paulo,

There are only 2 tips that are missing from your advice:

To enable REALLY internet sharing, Firewall from the Network preference panel
should be disabled on the main computer,

The others computers should be set to Using DHCP leaving blank all the optional field.


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Internet sharing Tips
Authored by: george47 on Jan 08, '03 06:14:23PM

excuse me, but you mean that you work WITHOUT a firewall?
I have to test my self this kind of configuration and now I'm using NetBarrier as sw firewall (in every computer) only with one computer at the time connected to the adsl.

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USB DSL + Airport + Wireless Access Point?
Authored by: shucks on Feb 14, '03 03:33:50AM

I've this problem that was ok before 10.2.4. But somehow it got broken after I installed 10.2.4 update. I have a G4 PowerBook that is connected to the net via USB SpeedTouch DSL. I have an linksys router+4 port switch (with the router disabled since i'm not connecting to internet via ethernet dsl) I have a Debian box connected to the 4 port switch. Now before all i have to do is connect to the internet and leave internet sharing off, put the debian to use the ip address of my g4 powerbook airport card ( as the gateway and it works! But now with the latest update I tried all sorts of combination (turning internet connection sharing for my USB DSL to share through ethernet (configured to and also setting to share through g4 airport (which is hopeless coz i can't even ping when i did this)) Phew that seems complicated to right. Anyone of you got any ideas what went wrong? P/S reason why i didn't just use a ethernet cable from my G4 to the linksys wireless switch is because i'm lazy to buy a new ethernet cable and am so stubborn and also would like to have my powerbook mobile at the same time).

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Use a second ethernet card for internet sharing
Authored by: psx on Mar 24, '03 03:29:38PM

Hey all -
I'm not sure if this is the best spot, but hopefully someone can help, or has run into this already.

I have a g3 powerbook that I'm using as a webserver. I'm running 10.2.4. The built-in ethernet is broken so up until jaguar, I've used a farallon fast EtherTX-10/100 Cardbus adapter. A brief history using this card and machine:

9.x - card works with farallon driver
10.? (public beta) - card didn't work at all, didn't even show up
10.0 - card worked! no extra drivers
10.1.x - still working! yippee!
10.2.x - kernel panic whenever card is near (in) machine!!

For now I have a linksys wireless card in there that works great with the sourceforge wireless driver. But it's rather slow and I want to hardwire it, since I don't need it to be wireless (it sits alone, on a desk, 5 feet from the router).

So does anyone have any idea what changed between 10.1.5 and 10.2?? Is there any driver that will get it working again? Anyone encounter this at all before?

Thanks a ton for any insight!

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