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tcllib_ip(n) 1.4 tcllib "Domain Name Service"


tcllib_ip - IPv4 and IPv6 address manipulation

Table Of Contents



This package provides a set of commands to help in parsing, displaying and comparing internet addresses. The package can handle both IPv4 (1) and IPv6 (2) address types.


::ip::version address

Returns the protocol version of the address (4 or 6), or -1 if the address is neither IPv4 or IPv6.

::ip::is class address

Returns true if the address is a member of the given protocol class. The class parameter may be either ipv4 or ipv6 This is effectively a boolean equivalent of the version command. The class argument may be shortened to 4 or 6.

::ip::equal address address

Compare two address specifications for equivalence. The arguments are normalized and the address prefix determined (if a mask is supplied). The normalized addresses are then compared bit-by-bit and the procedure returns true if they match.

::ip::normalize address

Convert an IPv4 or IPv6 address into a fully expanded version. There are various shorthand ways to write internet addresses, missing out redundant parts or digits. This procedure is the opposite of contract.

::ip::contract address

Convert a normalized internet address into a more compact form suitable for displaying to users.

::ip::distance ipaddr1 ipaddr2

This command computes the (integer) distance from IPv4 address ipaddr1 to IPv4 address ipaddr2, i.e. "ipaddr2 - ipaddr1"

   % ::ip::distance
::ip::nextIp ipaddr ?offset?

This command adds the integer offset to the IPv4 address ipaddr and returns the new IPv4 address.

   % ::ip::distance  4
::ip::prefix address

Returns the address prefix generated by masking the address part with the mask if provided. If there is no mask then it is equivalent to calling normalize

::ip::type address
::ip::mask address

If the address supplied includes a mask then this is returned otherwise returns an empty string.

::ip::prefixToNative prefix

This command converts the string prefix from dotted form (<ipaddr>/<mask> format) to native (hex) form. Returns a list containing two elements, ipaddress and mask, in this order, in hexadecimal notation.

   % ip::prefixToNative
   0x01010100 0xffffff00
::ip::nativeToPrefix nativeList|native ?-ipv4?

This command converts from native (hex) form to dotted form. It is the complement of ::ip::prefixToNative.

list nativeList (in)

List of several ip addresses in native form. The native form is a list as returned by ::ip::prefixToNative.

list native (in)

A list as returned by ::ip::prefixToNative.

The command returns a list of addresses in dotted form if it was called with a list of addresses. Otherwise a single address in dotted form is returned.

   % ip::nativeToPrefix {0x01010100 0xffffff00} -ipv4
::ip::intToString number ?-ipv4?

This command converts from an ip address specified as integer number to dotted form.

       ip::intToString 4294967295
::ip::toInteger ipaddr

This command converts a dotted form ip into an integer number.

   % ::ip::toInteger
::ip::toHex ipaddr

This command converts dotted form ip into a hexadecimal number.

   % ::ip::toHex
::ip::maskToInt ipmask

This command convert an ipmask in either dotted ( form or mask length form (24) into an integer number.

   ::ip::maskToInt 24
::ip::broadcastAddress prefix ?-ipv4?

This commands returns a broadcast address in dotted form for the given route prefix, either in the form "addr/mask", or in native form. The result is in dotted form.

   ::ip::broadcastAddress {0x01010100 0xffffff00}
::ip::maskToLength dottedMask|integerMask|hexMask ?-ipv4?

This command converts the dotted or integer form of an ipmask to the mask length form.

   ::ip::maskToLength 0xffffff00 -ipv4
   % ::ip::maskToLength
::ip::lengthToMask maskLength ?-ipv4?

This command converts an ipmask in mask length form to its dotted form.

   ::ip::lengthToMask 24
::ip::nextNet ipaddr ipmask ?count? ?-ipv4?

This command returns an ipaddress in the same position in the count next network. The default value for count is 1.

The address can be specified as either integer number or in dotted form. The mask can be specified as either integer number, dotted form, or mask length form.

The result is in hex form.

::ip::isOverlap prefix prefix...

This command checks if the given ip prefixes overlap. All arguments are in dotted "addr/mask" form. All arguments after the first prefix are compared against the first prefix. The result is a boolean value. It is true if an overlap was found for any of the prefixes.

  % ::ip::isOverlap
::ip::isOverlapNative ?-all? ?-inline? ?-ipv4? hexipaddr hexipmask hexiplist

This command is similar to ::ip::isOverlap, however the arguments are in the native form, and the form of the result is under greater control of the caller. If the option -all is specified it checks all addresses for overlap, not only until the first one is found. If the option -inline is specified the command returns the overlapping prefix instead of index values.

The result of the command is, depending on the specified options,

no options

The index of the first overlap found, or 0 if there is none.


A list containing the indices of all overlaps found, or an empty list if there are none.


The first overlapping prefix, or an empoty string if there is none.

-all -inline

A list containing the prefixes of all overlaps found, or an empty list if there are none.

  % ::ip::isOverlapNative 0x01010100 0xffffff00 {{0x02010001 0xffffffff}}
  % ::ip::isOverlapNative 0x01010100 0xffffff00 {{0x02010001 0xffffffff} {0x01010101 0xffffffff}}
::ip::ipToLayer2Multicast ipaddr

This command an converts ipv4 address in dotted form into a layer 2 multicast address, also in dotted form.

  % ::ip::ipToLayer2Multicast
::ip::ipHostFromPrefix prefix ?-exclude prefixExcludeList?

This command returns a host address from a prefix in the form "ipaddr/masklen", also making sure that the result is not an address found in the prefixExcludeList. The result is an ip address in dotted form.

::ip::reduceToAggregates prefixlist

This command finds nets that overlap and filters out the more specific nets. The prefixes are in either addr/mask form or in native format. The result is a list containing the non-overlapping ip prefixes from the input.

  % ::ip::reduceToAggregates { }
::ip::longestPrefixMatch ipaddr prefixlist ?-ipv4?

This command finds longest prefix match from set of prefixes, given a specific host address. The prefixes in the list are in either native or dotted form, whereas the host address is in either ipprefix format, dotted form, or integer form. The result is the prefix which is the most specific match to the host address.

  % ::ip::longestPrefixMatch { }
::ip::collapse prefixlist

This commands takes a list of prefixes and returns a list prefixes with the largest possible subnet masks covering the input, in this manner collapsing adjacent prefixes into larger ranges.

This is different from ::ip::reduceToAggregates in that the latter only removes specific nets from a list when they are covered by other elements of the input whereas this command actively merges nets into larger ranges when they are adjacent to each other.

% ::ip::collapse {}
::ip::subtract prefixlist

This command takes a list of prefixes, some of which are prefixed by a dash. These latter negative prefixes are used to punch holes into the ranges described by the other, positive, prefixes. I.e. the negative prefixes are subtracted frrom the positive ones, resulting in a larger list of describes describing the covered ranges only as positives.


% ip::version ::1
% ip::version
% ip::normalize 127/8
% ip::contract
% ip::normalize fec0::1
% ip::contract fec0:0000:0000:0000:0000:0000:0000:0001
% ip::equal
% ip::equal fec0::1/10 fec0::fe01/10


  1. Postel, J. "Internet Protocol." RFC 791, September 1981, (http://www.ietf.org/rfc/rfc791.txt)

  2. Hinden, R. and Deering, S., "Internet Protocol Version 6 (IPv6) Addressing Architecture", RFC 3513, April 2003 (http://www.ietf.org/rfc/rfc3513.txt)


Pat Thoyts

Bugs, Ideas, Feedback

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category dns of the Tcllib Trackers. Please also report any ideas for enhancements you may have for either package and/or documentation.

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See Also

inet(3), ip(7), ipv6(7)


internet address, ip, ipv4, ipv6, rfc 3513