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netmasks(4)			 File Formats			   netmasks(4)

       netmasks	- network mask database



       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,

       can  be used to specify that the	Class B	network 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,

       can  be	used  to  specify different netmasks in	different parts	of the  Class  B  network  number.  Addresses  through  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  through have a 26 bits in the subnet field.	Finally, all other ad-
       dresses	in  the	 range through have a	24 bit
       subnet field.

       Invalid entries are ignored.

       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.

       /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)


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