InternetSharing(8) BSD System Manager's Manual InternetSharing(8)
NAME
InternetSharing -- simple NAT/router configuration daemon
SYNOPSIS
InternetSharing -d
DESCRIPTION
InternetSharing is the back-end for the Internet Sharing feature. It is
responsible for configuring the network interfaces, the DHCP server
bootpd(8), the network address translation daemon natd(8), and the Inter-
net domain name server named(8). named(8) is run in caching-only mode
and allows the DHCP server to always offer the same DNS server address to
the DHCP clients, regardless of the value of the actual DNS server
addresses.
The single command line option -d places additional debugging information
to stdout/stderr.
InternetSharing is launched by launchd(8) both at start-up and when the
user turns Internet Sharing on in the Sharing preferences pane.
By default, InternetSharing configures the IP addresses for non-AirPort
interfaces starting at 192.168.2.1, walking up by one class C network
(subnet mask 255.255.255.0) for each subsequent interface i.e.
192.168.3.1, 192.168.4.1, 192.168.5.1, and so on. The AirPort interface
by default is assigned 10.0.2.1.
CONFIGURATION
InternetSharing reads the property list com.apple.nat.plist stored in the
/Library/Preferences/SystemConfiguration.
Details of the com.apple.nat.plist are subject to change and are not com-
pletely documented here. The plist is a contract between the Sharing
preferences pane and InternetSharing. Any details provided here are for
informational purposes only.
The plist is a dictionary with a single sub-dictionary called NAT con-
taining properties to control which interfaces to use and other settings.
It may also have a sub-dictionary called AirPort that is used to config-
ure the AirPort interface when it is put into access point mode.
One property worth mentioning is SharingNetworkNumberStart. This prop-
erty controls the behavior of InternetSharing when it configures IP
addresses for the local interfaces. The property is encoded as a string
containing the dotted decimal network IP address, assumed to be a class C
network. For example:
<key>SharingNetworkNumberStart</key>
<string>192.168.100.0</string>
If the SharingNetworkNumberStart appears directly in the NAT dictionary,
it controls the starting IP address chosen for the non-AirPort inter-
faces. If the property appears within the AirPort sub-dictionary, it
controls the IP address assigned to the AirPort interface.
The purpose of the property is to allow the user to avoid address colli-
sions with existing NAT'd networks.
SEE ALSO
bootpd(8), launchd(8), natd(8), named(8)
Mac OS X Feburary 26, 2007 Mac OS X
Mac OS X 10.6 - Generated Thu Sep 17 20:25:41 CDT 2009