How to switch the en0 and en1 assignments

Question

Level 1

0 points

How to switch the en0 and en1 assignments

Here's a challenge for you... 😉

I have a small (very small) customer that needs a server/router/firewall/etc.
So my plan for this customer was to take a Mac Mini, add a second network interface to it (Apple USB-to-Ethernet adaptor) and install Mac OS X Server on it.
Since the Built-in network adaptor is Gigabit, and considering the customer only has a 40/40 Mbit/s internet connection i would like to use the USB adaptor as the WAN adaptor an have the Giga adaptor on the LAN.
The only problem with this, is that the Gigabit adaptor is designated en0 and the USB adaptor is designated en1.
All the wizzards (like NAT & Firewall) in OS X 10.5 server assume that the WAN link is en0 and that en1 is the LAN interface.
I have tried switching the labels and positions of the interfacese in the '/Library/Preferences/SystemConfiguration/NetworkInterfaces.plist' file but with no luck.

Can anyone help me with this?

Best regards
Jeppe Schäfer
Denmark

24" iMac, MacBookAir, MacBook Pro, Mac OS X (10.5.5)

Posted on Nov 6, 2008 12:28 PM

Reply

Answer 1

Camelot

Level 9

54,339 points

Nov 6, 2008 3:21 PM in response to grundhunden

All the wizzards (like NAT & Firewall) in OS X 10.5 server assume that the WAN link is en0 and that en1 is the LAN interface.

Really? Everything I've seen shows that you get to nominate which interface is your external/WAN interface. There's no preconception.

How are you trying to configure the gateway?

Also, why are you trying to do it this way rather than through a dedicated hardware router? They probably cost less than the USB Ethernet adapter, too.

Reply

Answer 2

grundhunden Author

Level 1

0 points

Nov 9, 2008 12:01 PM in response to Camelot

I am quit sure i read that somewhere in the guides.
At the moment i can't seem to find the exact paragraph where i read it, but i did manage to find the following in the NAT configuration guide:

+You can configure your Mac OS X server to be a gateway to the Internet, which requires that your server have two Ethernet ports (en0 and en1). Ethernet en0 should be connected to the Internet+
+and en1 should be connected to your LAN.+

The reason for the approach is, that i would rather use the highly configurable firewall in OSX server that rely on some cheap router...
This way i would have an all-in-one box for my customer(s) - including only one point of failure.
By running storing data on External disks and using timemachine and allways keeping one Mac Mini ready at the office - hardware failures could quickly be resolved.

Also i am able to run Wireshark directly on the server AND router/firewall at once, making error tracking much easier than when using some closed router with simple logging.

Reply

Answer 3

andydvsn

Level 1

79 points

Nov 11, 2008 6:25 AM in response to grundhunden

This would be really useful for me as well, as I've got a very similar situation; Mac with one built-in ethernet and one additional one (PCI). I believe that you can shift out these files:

/Library/Preferences/SystemConfiguration/NetworkInterfaces.plist
/Library/Preferences/SystemConfiguration/preferences.plist

And everything should be recreated (stolen from an old Mac OS X Hints article: http://www.macosxhints.com/article.php?story=20051020014120761), but the problem is that there's no way to disable the built-in ethernet to cause the PCI interface (or in your case, USB) to become en0.

I haven't tried this, but perhaps you could try:

1. Moving those plist files out and rebooting (which will create a new NetworkInterfaces.plist)
2. Editing NetworkInterfaces.plist before going into Network in System Preferences
3. Rebooting again
4. Then try ifconfig in the Termainal and see what you're getting.

This is all guesswork on my part, though. Please post back if it works, because I'll be the next to try it!

Cheers,

Andy.

Reply

Answer 4

andydvsn

Level 1

79 points

Nov 26, 2008 8:08 AM in response to andydvsn

Replying to my own posting here, but I'd just like to confirm that this did actually work a charm.

You may also want to delete

/Library/Preferences/SystemConfiguration/coma.apple.network.identification.plist

as it contains a fair bit of IP information that was simply augmented after the reconfiguration. I rebooted into single user mode, deleted all three files and they were recreated cleanly when I booted into the desktop.

Reply