netmasks(4) Kernel Interfaces Manual netmasks(4)NAME
netmasks - DHCP server database
DESCRIPTION
The netmasks file is employed by joind, the DHCP server, to inform it about any networks having non-standard subnet masks. This file is
only needed on those platforms which don't provide a netmasks database, either as a text file or as an NIS map. Each network whose mask is
other than the standard A, B, or C mask should have an entry in this file. Each entry has two fields: the network and the mask. The net-
work may be written with or without zeros. See join.ipaddresses(4) for details.
This file also supports variable subnetting. If each subnetwork is further divided into subnetworks with a variable mask, the subnetworks
can also appear on the LHS.
FORMAT
Blank lines and lines beginning with "#" are ignored. Entries are separated from one another by newlines. Entries consist of two fields:
the network number (expressed as an IP address), and the network mask expressed as an IP address.
RELATED INFORMATION
Commands: joind(8), join.ipaddresses(4). delim off
netmasks(4)
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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 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 5.11 7 Jan 1997 netmasks(4)