1netmasks(4)                      File Formats                      netmasks(4)
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NAME

6       netmasks - network mask database
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SYNOPSIS

9       /etc/inet/netmasks
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12       /etc/netmasks
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DESCRIPTION

16       The  netmasks  file contains network masks used to implement IP subnet‐
17       ting. It supports both standard subnetting as specified in RFC-950  and
18       variable  length  subnetting as specified in RFC-1519. When using stan‐
19       dard subnetting there should be a single line for each network that  is
20       subnetted  in this file with the network number, any number of SPACE or
21       TAB characters, and the network mask to use on  that  network.  Network
22       numbers  and  masks  may  be specified in the conventional IP `.' (dot)
23       notation (like IP host addresses, but with zeroes for the  host  part).
24       For example,
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29             128.32.0.0    255.255.255.0
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35       can  be used to specify that the Class B network 128.32.0.0 should have
36       eight bits of subnet field and eight bits of host field, in addition to
37       the standard sixteen bits in the network field.
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40       When  using  variable  length subnetting, the format is identical. How‐
41       ever, there should be a line for each  subnet  with  the   first  field
42       being the subnet and the second field being the netmask that applies to
43       that subnet. The users of the database, such as ifconfig(1M), perform a
44       lookup  to  find  the longest possible matching mask. It is possible to
45       combine the  RFC-950 and  RFC-1519 form of subnet masks in the netmasks
46       file. For example,
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51             128.32.0.0     255.255.255.0
52             128.32.27.0    255.255.255.240
53             128.32.27.16   255.255.255.240
54             128.32.27.32   255.255.255.240
55             128.32.27.48   255.255.255.240
56             128.32.27.64   255.255.255.240
57             128.32.27.80   255.255.255.240
58             128.32.27.96   255.255.255.240
59             128.32.27.112  255.255.255.240
60             128.32.27.128  255.255.255.240
61             128.32.27.144  255.255.255.240
62             128.32.27.160  255.255.255.240
63             128.32.27.176  255.255.255.240
64             128.32.27.192  255.255.255.240
65             128.32.27.208  255.255.255.240
66             128.32.27.224  255.255.255.240
67             128.32.27.240  255.255.255.240
68             128.32.64.0    255.255.255.192
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74       can  be  used  to  specify different netmasks in different parts of the
75       128.32.0.0  Class  B  network  number.  Addresses  128.32.27.0  through
76       128.32.27.255  have  a subnet mask with 28 bits in the combined network
77       and subnet fields  (often referred to as the subnet field) and  4  bits
78       in   the   host  field.   Furthermore,  addresses  128.32.64.0  through
79       128.32.64.63 have a 26 bits in the subnet  field.  Finally,  all  other
80       addresses  in the range 128.32.0.0 through 128.32.255.255 have a 24 bit
81       subnet field.
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84       Invalid entries are ignored.
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SEE ALSO

87       ifconfig(1M), inet(7P)
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90       Postel, Jon, and Mogul, Jeff, Internet Standard  Subnetting  Procedure,
91       RFC  950,  Network  Information  Center, SRI International, Menlo Park,
92       Calif., August 1985.
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95       V. Fuller, T. Li, J. Yu, K. Varadhan, Classless  Inter-Domain   Routing
96       (CIDR):  an Address Assignment and Aggregation Strategy, RFC 1519, Net‐
97       work Information Center, SRI International, Menlo Park, Calif., Septem‐
98       ber 1993.
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101       T.  Pummill,  B.  Manning,  Variable  Length Subnet Table For IPv4, RFC
102       1878,  Network  Information  Center,  SRI  International,  Menlo  Park,
103       Calif., December 1995.
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NOTES

106       /etc/inet/netmasks is the official SVr4 name of the netmasks file.  The
107       symbolic link /etc/netmasks exists for BSD compatibility.
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111SunOS 5.11                        7 Jan 1997                       netmasks(4)