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Debian Project
15 May 1999


Utility for determining network masks


netmask - a netmask generation and conversion program


netmask [ options ] spec [ spec ... ]


This program accepts and produces a variety of common network address and netmask formats. Not only can it convert address and netmask notations, but it will optimize the masks to generate the smallest list of rules. This is very handy if you’ve ever configured a firewall or router and some nasty network administrator before you decided that base 10 numbers were good places to start and end groups of machines.


-h, --help
Print a summary of the options
-v, --version
Print the version number
-d, --debug
Print status/progress information
-s, --standard
Output address/netmask pairs
-c, --cidr
Output CIDR format address lists
-i, --cisco
Output Cisco style address lists
-r, --range
Output ip address ranges
-x, --hex
Output address/netmask pairs in hex
-o, --octal
Output address/netmask pairs in octal
-b, --binary
Output address/netmask pairs in binary
-n, --nodns
Disable DNS lookups for addresses


A spec is an address specification, it can look like:
One address.
All addresses from address1 to address2.
All addresses from address1 to address1+address2.
A group starting at address spanning mask.
An address is an internet network address, it can look like:
An internet hostname.
A standard dotted quad internet address notation.
100 A decimal number (100 in this case).
0100 An octal number preceded by "0" (64 in this case).
0x100 A hexadecimal number preceded by "0x" (256 in this case).
A mask is a network mask, it can look like:
A dotted quad netmask (netmask will complain if it is not a valid netmask).
A Cisco style inverse netmask (with the same checks).
8 The number of bits set to one from the left (CIDR notation).
010 The number of bits set to one from the left in octal.
0x10 The number of bits set to one from the left in hexadecimal.


netmask was written by Robert Stone. Some algorithm design and optimization was provided by Tom Lear. This manual page was written by Robert Stone.


Let me know if you find any. This man page is a bit more simplistic than I’d like, but I’ve forgotten most of the groff I once knew.


ipchains(1), ipfwadm(8), netstat(8), route(8), routed(8), gated(8), tcpd(8)
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