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IPAliases.conf(5)           BSD File Formats Manual          IPAliases.conf(5)

NAME
     IPAliases -- format of the IP aliases configuration file

DESCRIPTION
     The file /etc/IPAliases.conf consists of newline separated ASCII records, containing two or three
     colon-separated fields of the form
           interface  name of the interface
           IP-addr    the IP address to be associated with interface
           netmask    the optional netmask to be associated with IP-addr

     The interface field is the name of network interface that will host the IP alias. The interface field
     should consist of three or four charcters. The interface must be "lo0" (implying the loopback inter-face), interface),
     face), or an interface returned by the ifconfig -l -u command. For example, the built-in ethernet
     interface is typically named ``en0''.

     The IP-addr field is the IP address to host on the indicated interface. The IP-addr field must be a
     valid IP address in dotted-decimal notation.  For example, a valid IP address could be 10.0.100.253 or
     196.221.43.3.

     In Mac OS X Server 10.4 and later, CIDR notation is also supported.  If this notation is used, the net-mask netmask
     mask field must be not be present.  Examples of valid CIDR notation include 10.0.100.253/16 and
     196.221.43.3/24.

     The netmask field is an optional field that defines the netmask associated with IP-addr.  If this field
     is omitted and IP-addr does not specify the mask via CIDR, the given IP-addr will use a default mask of
     255.255.255.255 to avoid a common configuration problem: new addresses on the same subnet as the first
     address assigned to interface must use this ``all ones'' format. (See the alias entry in ifconfig(8)
     for more details.) The netmask field must be a valid mask in dotted-decimal notation, i.e. leading
     "one" bits followed by "zero" bits.  For example, 192.0.0.0, 255.255.0.0, and 255.255.224.0 are "valid"
     netmasks, but 10.0.100.253 and 10.255.255.255 are not.

     In addition to defining the configuration file, IP aliases must be enabled in /etc/hostconfig by defin-ing defining
     ing the IPALIASES record to "-YES-".

     Addresses assigned to non-loopback interfaces are pinged by default to determine their existence on the
     network. To eliminate this step and force the acquisition of the addresses, define the PINGIPALIASES
     record to "-NO-" in /etc/hostconfig.

     Changes made to this file will not be activated until the next system restart. To protect the system, a
     simple file permission and ownership check is performed before loading the configuration file: the file
     is only loaded if it is owned by root and is not writeable by group or other. See chmod(2) for an
     explanation of file modes and how to change them.

EXAMPLES
     A valid configuration file might contain

           lo0:10.254.0.10/16
           lo0:10.254.0.11/16
           en0:10.254.0.91
           en1:10.254.0.206
           en2:10.254.0.101:255.255.0.0
           en2:10.254.0.191:255.255.0.0

FILES & FOLDERS
     /System/Library/StartupItems/IPAliases
     /etc/IPAliases.conf
     /etc/hostconfig
     /var/log/IPAliases.log

SEE ALSO
     ifconfig(8), ping(8)

Mac OS X Server                  May 13, 2006                  Mac OS X Server