Net::Netmask(3)

NAME
 Net::Netmask - parse, manipulate and lookup IP network blocks

SYNOPSIS
 use Net::Netmask;

 $block = Net::Netmask->safe_new(network block)
 $block = Net::Netmask->safe_new(network block, netmask)
 $block = Net::Netmask->new2(network block)
 $block = Net::Netmask->new2(network block, netmask)
 $block = Net::Netmask->new(network block)   # Don't use in new code!
 $block = Net::Netmask->new(network block, netmask)   # Don't use in new code!

 print $block;                      # a.b.c.d/bits or 1:2:3::4/bits
 print $block->base()
 print $block->mask()
 print $block->hostmask()
 print $block->bits()
 print $block->size()
 print $block->maxblock()
 print $block->broadcast()
 print $block->next()
 print $block->match($ip);
 print $block->nth(1, [$bitstep]);
 print $block->protocol();

 if ($block->sameblock("network block")) ...
 if ($block->cmpblocks("network block")) ...

 $newblock = $block->nextblock([count]);

 for $ip ($block->enumerate([$bitstep])) { }

 for $zone ($block->inaddr()) { }

 my $table = {};
 $block->storeNetblock([$table])
 $block->deleteNetblock([$table])
 @missingblocks = $block->cidrs2inverse(@blocks)

 $block = findNetblock(ip, [$table])
 $block = findOuterNetblock(ip, [$table])
 @blocks = findAllNetblock(ip, [$table])
 if ($block->checkNetblock([$table]) ...
 $block2 = $block1->findOuterNetblock([$table])
 @blocks = dumpNetworkTable([$table])

 @blocks = range2cidrlist($beginip, $endip);
 @blocks = cidrs2cidrs(@blocks_with_dups)

 @listofblocks = cidrs2contiglists(@blocks);

 @blocks = sort @blocks
 @blocks = sort_network_blocks(@blocks)

 @sorted_ip_addrs = sort_by_ip_address(@unsorted_ip_addrs)

DESCRIPTION
Net::Netmask parses and understands IPv4 and IPv6 CIDR blocks (see <https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing> for more information on CIDR blocks). It's built with an object-oriented interface, with functions being methods that operate on a Net::Netmask object.

These methods provide nearly all types of information about a network block that you might want.

There are also functions to insert a network block into a table and then later lookup network blocks by IP address using that table. There are functions to turn a IP address range into a list of CIDR blocks. There are functions to turn a list of CIDR blocks into a list of IP addresses.

There is a function for sorting by text IP address.

All functions understand both IPv4 and IPv6. Matches, finds, etc, will always return false when an IPv4 address is matched against an IPv6 address.

IPv6 support was added in 1.9104.

CONSTRUCTING
Net::Netmask objects are created with an IP address and optionally a mask. There are many forms that are recognized:

'216.240.32.0/24'
    The preferred IPv6 form.

'216.240.32.0:255.255.255.0'
'216.240.32.0-255.255.255.0'
'216.240.32.0', '255.255.255.0'
'216.240.32.0', '0xffffff00'
'216.240.32.0 - 216.240.32.255'
'216.240.32.4'
    A /32 block.

'default' or 'any'
    0.0.0.0/0 (the default route)

'216.240.32.0#0.0.31.255'
    A hostmask (as used by Cisco access-lists - that is, the hostmask is the bitwise inverse of a netmask).

'2001:db8:1234:5678::/64'
    The preferred IPv6 form.

'2001:db8:1234:5678::9876'
    A /128 block.

'default6' or 'any6'
    ::/0 (the default route)

There are two constructor methods: "new" and "safe_new" (also known as "new2").

"safe_new" differs from "new" in that it will return undef for invalid netmasks, while "new" will return a netmask object even if the constructor could not figure out what the network block should be.

With "new", the error string can be found as $block->{'ERROR'}. With "safe_new" the error can be found as Net::Netmask::errstr or $Net::Netmask::error.

IMPORTANT: You want to use "safe_new" or "new2" ("new2" is a synonym for "new") in new code!

As of version 2.000, the following abbreviated IPv4 netblocks are not accepted by default, but can be accepted with options.

'216.240.32'
    Always a /24 block.

'216.240'
    Always a /16 block.

'140'
    Always a /8 block.

'216.240.32/24'
'216.240/16'

To accept these, you can call the constructor with a "shortnet" option set to a true value. Example:

  my $block = Net::Netmask->safe_new("216.240/16", shortnet => 1);

For compatibility with older codebases, it's also possible to change the default to use the old behavior. To do this, you can set the $Net::Netmask::SHORTNET_DEFAULT variable to a true value. It is recommended that this be done by localizing the variable. Example:

  local $Net::Netmask::SHORTNET_DEFAULT = 1
  my $block = Net::Netmask->safe_new("216.240/16");

Please be aware that there are security implications to this as other Perl modules, system libraries, or utilities may not parse these addresses the same way. This is why the default was changed.

For instance:

  perl -MNet::Netmask -E "say Net::Netmask->safe_new("10.20", shortnet => 1)"

Will print "10.2.0.0/16". However:

  perl -MSocket -E "say inet_ntoa(inet_aton('10.20'))"

Will often print "10.0.0.20" which is obviously very different, and if the Net::Netmask module was used to check an IP aggainst an ACL, and then another program was executed (that uses inet_aton(), for instance), the ACL processing might not match the connection.

Thus, it is advised to use this with caution.

METHODS

->desc()
    Returns a description of the network block. Eg: "216.240.32.0/19" or "2001:db8:1234::/48". This is also available as overloaded stringification.

->base()
    Returns base address of the network block as a string. Eg: "216.240.32.0". or "2001:db8:1234::/48". Base does not give an indication of the size of the network block.

->mask()
    Returns the netmask as a string. Eg: "255.255.255.0" or "ffff:ffff:ffff:ffff::"

->hostmask()
    Returns the host mask which is the opposite of the netmask. Eg: "0.0.0.255" or "::ffff:ffff:ffff:ffff".

->bits()
    Returns the netmask as a number of bits in the network portion of the address for this block. Eg: 24.

->size()
    Returns the number of IP addresses in a block. Eg: 256. For IPv6 addresses, this will be a Math::BigInt object.

->broadcast()
    The blocks broadcast address. (The last IP address inside the block.) Eg: 192.168.1.0/24 => 192.168.1.255 or 2001:db8::/64 => 2001:db8::ffff:ffff:ffff:ffff

->next()
    The first IP address following the block. (The IP address following the broadcast address.) Eg: 192.168.1.0/24 => 192.168.2.0 or 2001:db8:0:1::/64 => 2001:db8:0:2::/64

->first() & ->last()
    Synonyms for ->base() and ->broadcast()

->protocol()
    Added in version 1.9102.

    Returns the address family/protocol represented by the block. Either 'IPv4' or 'IPv6'.

->match($ip)
    Returns a true if the IP number $ip matches the given network. That is, a true value is returned if $ip is between base() and broadcast(). For example, if we have the network 192.168.1.0/24, then

      192.168.0.255 => 0
      192.168.1.0   => "0 "
      192.168.1.1   => 1
      ...
      192.168.1.255 => 255

    $ip should be a dotted-quad (eg: "192.168.66.3") or an IPv6 address in standard notation (eg: "2001:db8::1").

    It just happens that the return value is the position within the block. Since zero is a legal position, the true string "0 " is returned in it's place. "0 " is numerically zero though. When wanting to know the position inside the block, a good idiom is:

      $pos = $block->match($ip) or die;
      $pos += 0;

->maxblock()
    Much of the time, it is not possible to determine the size of a network block just from it's base address. For example, with the network block '216.240.32.0/27', if you only had the '216.240.32.0' portion you wouldn't be able to tell for certain the size of the block. '216.240.32.0' could be anything from a '/23' to a '/32'. The maxblock() method gives the size of the largest block that the current block's address would allow it to be. The size is given in bits. Eg: 23.

->enumerate([$bitstep)
    Returns a list of all the IP addresses in the block. Be very careful not to use this function of large blocks. The IP addresses are returned as strings. Eg: '216.240.32.0', '216.240.32.1', ... '216.240.32.255'.

    If the optional argument is given, step through the block in increments of a given network size. To step by 4, use a bitstep of 30 (as in a /30 network).

    Note that for IPv6, this will return failure if more than 1,000,000,000 addresses would be returned.

->nth($index, [$bitstep])
    Returns the nth element of the array that enumerate would return if it were called. So, to get the first usable address in a block, use nth(1). To get the broadcast address, use nth(-1). To get the last usable address, use nth(-2).

->inaddr()
    Returns an inline list of tuples.

    For IPv4:

    There is a tuple for each DNS zone name (at the /24 level) in the block. If the block is smaller than a /24, then the zone of the enclosing /24 is returned.

    Each tuple contains: the DNS zone name, the last component of the first IP address in the block in that zone, the last component of the last IP address in the block in that zone.

    Examples: the list returned for the block '216.240.32.0/23' would be: '32.240.216.in-addr.arpa', 0, 255, '33.240.216.in-addr.arpa', 0, 255. The list returned for the block '216.240.32.64/27' would be: '32.240.216.in-addr.arpa', 64, 95.

    For IPv6:

    A list is returned with each DNS zone name at the shortest-prefix length possible. This is not returned as a tuple, but just a list of strings.

    Examples: the list returned for the block '2002::/16' would be a one element list, containing just 2.0.0.2.ip6.arpa'. The list for '2002::/17' would return a two element list containing '0.2.0.0.2.ip6.arpa' and '1.2.0.0.2.ip6.arpa'.

->nextblock([$count])
    Without a $count, return the next block of the same size after the current one. With a count, return the Nth block after the current one. A count of -1 returns the previous block. Undef will be returned if out of legal address space.

->sameblock($block)
    Compares two blocks. The second block will be auto-converted from a string if it isn't already a Net::Netmask object. Returns 1 if they are identical.

->cmpblocks($block)
    Compares two blocks. The second block will be auto-converted from a string if it isn't already a Net::Netmask object. Returns -1, 0, or 1 depending on which one has the lower base address or which one is larger if they have the same base address.

->contains($block)
    Compares two blocks. The second block will be auto-converted from a string if it isn't already a Net::Netmask object. Returns 1 if the second block fits inside the first block. Returns 0 otherwise.

->storeNetblock([$t])
    Adds the current block to an table of network blocks. The table can be used to query which network block a given IP address is in.

    The optional argument allows there to be more than one table. By default, an internal table is used. If more than one table is needed, then supply a reference to a HASH to store the data in.

->deleteNetblock([$t])
    Deletes the current block from a table of network blocks.

    The optional argument allows there to be more than one table. By default, an internal table is used. If more than one table is needed, then supply a reference to a HASH to store the data in.

->checkNetblock([$t])
    Returns true of the netblock is already in the network table.

->tag($name [, $value])
    Tag network blocks with your own data. The first argument is the name of your tag (hash key) and the second argument (if present) is the new value. The old value is returned.

->split($parts)
    Splits a netmask into a number of sub netblocks. This number must be a base 2 number (2,4,8,16,etc.) and the number must not exceed the number of IPs within this netmask.

    For instance,

      Net::Netmask->safe_new( '10.0.0.0/24' )->split(2)

    is equivilent to

      ( Net::Netmask( '10.0.0.0/25'), Net::Netmask( '10.0.0.128/25' ) )

METHOD/FUNCTION COMBOS

findOuterNetblock(ip, [$t])
    Search the table of network blocks (created with storeNetBlock) to find if any of them contain the given IP address. The IP address can either be a string or a Net::Netmask object (method invocation). If more than one block in the table contains the IP address or block, the largest network block will be the one returned.

    The return value is either a Net::Netmask object or undef.

cidrs2inverse(block, @listOfBlocks)
    Given a block and a list of blocks, cidrs2inverse() will return a list of blocks representing the IP addresses that are in the block but not in the list of blocks. It finds the gaps.

    The block will be auto-converted from a string if it isn't already a Net::Netmask object. The list of blocks should be Net::Netmask objects.

    The return value is a list of Net::Netmask objects.

OVERLOADING

""  Strinification is overloaded to be the ->desc() method.

cmp Numerical and string comparisons have been overloaded to the ->cmpblocks() method. This allows blocks to be sorted without specifying a sort function.

FUNCTIONS

sort_by_ip_address
    This function is included in "Net::Netmask" simply because there doesn't seem to be a better place to put it on CPAN. It turns out that there is one method for sorting dotted-quads ("a.b.c.d") that is faster than all the rest. This is that way. Use it as "sort_by_ip_address(@list_of_ips)". That was the theory anyway. Someone sent a faster version ...

    This method also will sort IPv6 addresses, but is not performance optimized. It is correct, however.

sort_network_blocks
    This function is a function to sort Net::Netmask objects. It's faster than the simpler "sort @blocks" that also works.

findNetblock(ip, [$t])
    Search the table of network blocks (created with storeNetBlock) to find if any of them contain the given IP address. The IP address is expected to be a string. If more than one block in the table contains the IP address, the smallest network block will be the one returned.

    The return value is either a Net::Netmask object or undef.

findAllNetblock(ip, [$t])
    Search the table of network blocks (created with storeNetBlock) to find if any of them contain the given IP address. The IP address is expected to be a string. All network blocks in the table that contain the IP address will be returned.

    The return value is a list of Net::Netmask objects.

dumpNetworkTable([$t])
    Returns a list of the networks in a network table (as created by ->storeNetblock()).

range2cidrlist($startip, $endip)
    Given a range of IP addresses, return a list of blocks that span that range.

    For example, range2cidrlist('216.240.32.128', '216.240.36.127'), will return a list of Net::Netmask objects that correspond to:

        216.240.32.128/25
        216.240.33.0/24
        216.240.34.0/23
        216.240.36.0/25

cidrs2contiglists(@listOfBlocks)
    "cidrs2contiglists" will rearrange a list of Net::Netmask objects such that contiguous sets are in sublists and each sublist is discontiguous with the next.

    For example, given a list of Net::Netmask objects corresponding to the following blocks:

        216.240.32.128/25
        216.240.33.0/24
        216.240.36.0/25

    "cidrs2contiglists" will return a list with two sublists:

        216.240.32.128/25 216.240.33.0/24

        216.240.36.0/25

    Overlapping blocks will be placed in the same sublist.

cidrs2cidrs(@listOfBlocks)
    "cidrs2cidrs" will collapse a list of Net::Netmask objects by combining adjacent blocks into larger blocks. It returns a list of blocks that covers exactly the same IP space. Overlapping blocks will be collapsed.

AUTHORS
Joelle Maslak <jmaslak@antelope.net> (current maintainer)

David Muir Sharnoff (original creator/author)

LICENSE
Copyright (C) 1998-2006 David Muir Sharnoff.

Copyright (C) 2011-2013 Google, Inc.

Copyright (C) 2018-2021 Joelle Maslak

This module may be used, modified and redistributed under the same terms as Perl itself.