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 subnetting. It supports both standard subnetting as specified in RFC-950 and
       variable length subnetting as specified in RFC-1519. When using standard 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) notation (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. However, there should be a line for each subnet with the  first field being
       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  net-
       masks 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
       addresses 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,
       Network Information Center, SRI International, Menlo Park, Calif., September 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 5.10                                                          7 Jan 1997                                                         netmasks(4)