netmask - Man Page

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.


A decimal number (100 in this case).


An octal number preceded by "0" (64 in this case).


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).


The number of bits set to one from the left (CIDR notation).


The number of bits set to one from the left in octal.


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.

See Also

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


15 May 1999 Debian Project Debian Linux