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OS X - Operating System General OS operation information and support

Internet sharing is a slippery beast

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Member Since: Jul 16, 2011
Posts: 2
bwanaaa is on a distinguished road

bwanaaa is offline
A simple checkbox and a menu allow you to share your internet connection (no matter which interface you get it on) with any other interface. (theoretically)
But the guts of this is a little confusing. This page
man page InternetSharing section 8
describes InternetSharing, a process which reads the property list stored in the /Library/Preferences/SystemConfiguration.

First question:
why is the airport singled out with its own special entry in the plist? I understand the entries for primary interface (the source) and the sharing devices (the targets) But who cares if airport is enabled in this plist if you are setting up a nat between ethernet and bluetooth for example.

Second question:
why does it allow sharing of ethernet connection with ethernet connection and then give you a warning that your isp will hate you? (it also allows fire wire with firewire) it doesnt allow bluetooth-bluetooth or airport-airport=> the menu entries for self reference disappear.

Third question:
How do you change the default network when you share the ethernet through your airport? InternetSharing configures the IP addresses for non-AirPort interfaces starting at and the SharingNetworkNumberStart property allows you to change that. The AirPort interface by default is assigned How to change?

Fourth question:
If you only have one ethernet jack on a macbook how could you possibly have more than one interface?. InternetSharing configures the IP addresses for non-AirPort interfaces starting at, walking up by one class C network (subnet mask for each subsequent interface i.e.,,, and so on. Is this to address the possibility of a macpro or an xserve with multiple nics?

Tnx to the guru who shares his/her(?) knowledge.If it is a her I'd REALLY to meet her.
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Member Since: Jul 16, 2011
Posts: 2
bwanaaa is on a distinguished road

bwanaaa is offline
problems solved.
1) the airport is not like the other interfaces
2) the hard connections are less likely to connect to themselves-you actually have to WIRE them and nobody would do that
3)edit the bootpd.plist
4) usb adapters
tnx. i solved the problem. even tho i turned off the firewall in the gui, ipfw was still running. sudo ipfw list gave the same list of rules regardless whether i had firewall on or off. dont know how i managed to achieve that!

i looked to noobproof and turned off the rule for blocking port 80. now it works, at east for web surfing.
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