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netmasks(4)			 File Formats			   netmasks(4)

NAME
       netmasks	- network mask database

SYNOPSIS
       /etc/inet/netmasks

       /etc/netmasks

DESCRIPTION
       The  netmasks  file contains network masks used to implement IP subnet-
       ting. It	supports both standard subnetting as specified in RFC-950  and
       variable	 length	 subnetting as specified in RFC-1519. When using stan-
       dard subnetting there should be a single	line for each network that  is
       subnetted  in this file with the	network	number,	any number of SPACE or
       TAB characters, and the network mask to use on  that  network.  Network
       numbers and masks may be	specified in the conventional IP `.' (dot) no-
       tation (like IP host addresses, but with	zeroes	for  the  host	part).
       For example,

	     128.32.0.0	   255.255.255.0

       can  be used to specify that the	Class B	network	128.32.0.0 should have
       eight bits of subnet field and eight bits of host field,	in addition to
       the standard sixteen bits in the	network	field.

       When  using  variable  length subnetting, the format is identical. How-
       ever, there should be a line for	each subnet with the  first field  be-
       ing  the	 subnet	and the	second field being the netmask that applies to
       that subnet. The	users of the database, such as ifconfig(1M), perform a
       lookup  to  find	 the longest possible matching mask. It	is possible to
       combine the  RFC-950 and	 RFC-1519 form of subnet masks in the netmasks
       file. For example,

	     128.32.0.0	    255.255.255.0
	     128.32.27.0    255.255.255.240
	     128.32.27.16   255.255.255.240
	     128.32.27.32   255.255.255.240
	     128.32.27.48   255.255.255.240
	     128.32.27.64   255.255.255.240
	     128.32.27.80   255.255.255.240
	     128.32.27.96   255.255.255.240
	     128.32.27.112  255.255.255.240
	     128.32.27.128  255.255.255.240
	     128.32.27.144  255.255.255.240
	     128.32.27.160  255.255.255.240
	     128.32.27.176  255.255.255.240
	     128.32.27.192  255.255.255.240
	     128.32.27.208  255.255.255.240
	     128.32.27.224  255.255.255.240
	     128.32.27.240  255.255.255.240
	     128.32.64.0    255.255.255.192

       can  be	used  to  specify different netmasks in	different parts	of the
       128.32.0.0  Class  B  network  number.  Addresses  128.32.27.0  through
       128.32.27.255  have  a subnet mask with 28 bits in the combined network
       and subnet fields  (often referred to as	the subnet field) and  4  bits
       in   the	  host	field.	 Furthermore,  addresses  128.32.64.0  through
       128.32.64.63 have a 26 bits in the subnet field.	Finally, all other ad-
       dresses	in  the	 range 128.32.0.0 through 128.32.255.255 have a	24 bit
       subnet field.

       Invalid entries are ignored.

SEE ALSO
       ifconfig(1M), inet(7P)

       Postel, Jon, and	Mogul, Jeff, Internet Standard	Subnetting  Procedure,
       RFC  950,  Network  Information	Center,	SRI International, Menlo Park,
       Calif., August 1985.

       V. Fuller, T. Li, J. Yu,	K. Varadhan, Classless	Inter-Domain   Routing
       (CIDR):	an Address Assignment and Aggregation Strategy,	RFC 1519, Net-
       work Information	Center,	SRI International, Menlo Park, Calif., Septem-
       ber 1993.

       T.  Pummill,  B.	 Manning,  Variable  Length Subnet Table For IPv4, RFC
       1878,  Network  Information  Center,  SRI  International,  Menlo	 Park,
       Calif., December	1995.

NOTES
       /etc/inet/netmasks is the official SVr4 name of the netmasks file.  The
       symbolic	link /etc/netmasks exists for BSD compatibility.

SunOS 5.9			  7 Jan	1997			   netmasks(4)

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | NOTES

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