SUBCALC(1) BSD General Commands Manual SUBCALC(1)NAMEsubcalc — Advanced IP/IPv6 subnet calculation and discovery
SYNOPSISsubcalc [address family] [address] [print]
subcalc [address family] [address] [netmask] [mask] [print]
subcalc [address family] [address] [prefixlen] [len] [print]
subcalc [address family] [hosts] [number]
subcalc [int6] [address] [hostname]
subcalc [arpa6] [address] [hostname]
subcalc [stf] [address family] [address]
DESCRIPTION
The subcalc utility is used for subnet calculation and IPv6 DNS PTR
record generation. subcalc takes command line arguments in a similar
format to ifconfig(8) so the synopsis should be familiar to the user.
Given an address family, address and a netmask/prefix length, subcalc
will calculate the number of hosts and address ranges of the specific
network. Specifying the ``print'' option to to the end of the command
line will result in every single network address for the specified net‐
work being printed to stdout.
subcalc was designed for network engineers which setup fine grained fire‐
walls, packet filters, access control lists and network subdivisions for
both IP and IPv6 servers and networks.
The following options are available:
address_family
Specify the address family which affects interpretation of the
remaining parameters. Since subcalc can handle subnet calcula‐
tions in different protocols with different naming schemes, spec‐
ifying the address family is recommended. The address or proto‐
col families currently supported are “inet” and “inet6”.
address
For the DARPA-Internet family, the address is an Internet address
expressed in the Internet standard “dot notation”.
It is also possible to use the CIDR notation (also known as the
slash notation) to include the netmask. That is, one can specify
an address like 192.168.0.1/16.
For “inet6” family, it is also possible to specify the prefix
length using the slash notation, like ::1/128. See the prefixlen
parameter below for more information.
arpa6 address
Generate an ARPA6 PTR record which the popular DNS server
``BIND'' will understand. In order for the components of the PTR
record to be complete, a hostname must be specified as well.
hosts number
Specify the number of nodes or addresses on a network and subcalc
will calculate an appropriate network subdivision and bits. This
is used for netmask discovery. NOTE: currently subcalc calculates
the subdivision for one network. In some cases it may be more
efficient to use more then one network subdivision.
int6 address
Generate an INT6 PTR record which the popular DNS server ``BIND''
will understand. In order for the components of the PTR record to
be complete, a hostname must be specified as well.
netmask mask
Specify how much of the address to reserve for subdividing net‐
works into sub-networks. The mask includes the network part of
the local address and the subnet part, which is taken from the
host field of the address. The mask can be specified as a single
hexadecimal number with a leading ‘0x’, or with a dot-notation
Internet address. The mask contains 1's for the bit positions in
the 32-bit address which are to be used for the network and sub‐
net parts, and 0's for the host part. The mask should contain at
least the standard network portion, and the subnet field should
be contiguous with the network portion.
The netmask can also be specified in CIDR notation after the
address. See the address option above for more information.
prefixlen len
Specify that len bits are reserved for subdividing networks into
sub-networks. The len must be an integer, and for syntactical
reason it must be between 0 to 128. It is almost always 64 under
the current IPv6 assignment rule. If the parameter is omitted,
64 is used.
The prefix can also be specified using the slash notation after
the address. See the address option above for more information
print causes each address in the specified network to be printed to
stdout, one address per line. Regular subnet calculation is
still performed, however each line of the standard calculation
output is prefixed by a ``;'' character. This makes it easy for
standard subnet calculations to be filtered out, in the event
that network lists need to be generated.
stf If the address family is inet, translate the argument as an IPv4
address which will be converted into the arbitrary IPv6 ``/48''
(6to4 rfc3056) network designation. If the family is inet6,
translate the argument as an IPv6 network or address specifica‐
tion which will be converted into it's arbitrary IPv4 parent
address.
EXAMPLES
To calculate the network range, number of hosts, prefixlen or CIDR and
netmask for the 10.0.0.1/24 (255.255.255.0) network.
% subcalc inet 10.0.0.1/24
Anyone of the following will achieve the exact same thing:
% subcalc inet 10.0.0.1 netmask 255.255.255.0
% subcalc inet 10.0.0.1 netmask 0xffffff00
% subcalc inet 10.0.0.1 prefixlen 24
To generate a list of nodes for the specified network one could use any‐
one of the following methods:
% subcalc inet 10.0.0.1/24 print
% subcalc inet 10.0.0.1 netmask 255.255.255.0 print
% subcalc inet 10.0.0.1 netmask 0xffffff00 print
% subcalc inet 10.0.0.1 prefixlen 24 print
Arbitrarily, the same thing can be done for IPv6. To calculate the net‐
work range, number of hosts, prefixlen etc for the
3ffe:beef:13e1:4c92::cd90/48 network, one could use any of the following:
% subcalc inet6 3ffe:beef:13e1:4c92::cd90/48
% subcalc inet6 3ffe:beef:13e1:4c92::cd90 netmask ffff:ffff:ffff::
% subcalc inet6 3ffe:beef:13e1:4c92::cd90 prefixlen 48
Likewise for printing each node of a network:
% subcalc inet6 3ffe:beef:13e1:4c92::cd90/48 print
% subcalc inet6 3ffe:beef:13e1:4c92::cd90 prefixlen 48 print
IP version 4 PTR records (records which map an address to a canonical
name) contain a portion which has a reversed version of the IP octet pre‐
fixing the in-addr.arpa. zone. For example, an RFC 1035 PTR record for
10.0.0.1 would look like:
1.0.0.10.in-addr.arpa. IN PTR canonical.name.org.
The first section of this PTR record is called the ``owner'':
1.0.0.10.in-addr.arpa.
For IP version 6, rather then reversing each octet, PTR records require
that each ``nibble'' or 4 bit address subdivision be reversed. For exam‐
ple, the owner section of a PTR record for the IPv6 address
3ffe:beef:13e1:4c92::cd90 would be:
0.9.d.c.0.0.0.0.0.0.0.0.0.0.0.0.2.9.c.4.1.e.3.1.f.e.e.b.e.f.f.3.ip6.arpa.
Creating PTR record for IP version 6 addresses can be tedious and more
prone to error. subcalc has the capability to automatically subdivide
the IPv6 address into nibbles and reverse them into a PTR record like
format. An example on how this might be achieved is:
% subcalc arpa6 3ffe:beef:13e1:4c92::cd90 canonical.name.org.
% subcalc int6 3ffe:beef:13e1:4c92::cd90 canonical.name.org.
If you wanted to calculate a subdivision for a network given the number
of nodes or hosts, you could do:
% subcalc inet hosts 23
The next highest network subdivision in this case would be a ``/27''
which has 32 hosts. The netmask for this network would be:
255.255.255.224.
Given an IPv4 address, figure out the 6to4 IPv6 ``/48'' network associ‐
ated with it.
% subcalc stf inet 204.55.55.1
Given an IPv6 network or address, figure out what IPv4 address represents
the parent for the network.
% subcalc stf inet6 2002:cc37:3701::/48
% subcalc stf inet6 2002:cc37:3701:bc38::4081
AUTHOR
The subcalc utility and this man page was written by Christian S.J.
Peron. Send any bugs or patches to (maneo@bsdpro.com).
SEE ALSOifconfig(8), inet(4), netintro(4), netstat(1), stf(4)BSD August 22, 2003 BSD
