InternetSharing(8) BSD System Manager's Manual InternetSharing(8)

NAME
     IInntteerrnneettSShhaarriinngg - simple NAT/router configuration daemon

SYNOPSIS
     IInntteerrnneettSShhaarriinngg -d

DESCRIPTION
     IInntteerrnneettSShhaarriinngg 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.

     IInntteerrnneettSShhaarriinngg is launched by launchd(8) both at start-up and when the
     user turns Internet Sharing on in the Sharing preferences pane.

     By default, IInntteerrnneettSShhaarriinngg 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.

CCOONNFFIIGGUURRAATTIIOONN
     IInntteerrnneettSShhaarriinngg 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 IInntteerrnneettSShhaarriinngg. 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 AAiirrPPoorrtt 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 IInntteerrnneettSShhaarriinngg 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:
             SharingNetworkNumberStart
             192.168.100.0

     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