Ray Mroz


LinkLocal::IPv4::Interface - IPv4 link-local interface wrapper


  use LinkLocal::IPv4::Interface;
  my $if_obj = LinkLocal::IPv4::Interface->new('eth0');
  # TODO: finalize method signature and process
  $if_obj->if_config( $arg_a, $arg_b ); 


This package represents a lightweight, pure Perl implementation of the specification as outlined in RFC-3927, Dynamic Configuration of IPv4 Link-Local Addresses. This standard details a mechanism which provides a means of enabling automatic IPv4 address allocations to network addressable entities and devices which by happenstance or design find themselves on an unmanaged, ad hoc IP network with no other means of acquiring a fully routable, unicast IPv4 address. As the name implies, link-local IPv4 addresses are non-routable in the IANA reserved 169.254/16 prefix, with all participating devices connected to the same physical link; this fact all but dictates that such networks are typically small. Home networks or other such small environments are well suited to the deployment of this standard. While there are, in theory, upwards of 65,024 addresses available in the range for allocations, the reality is that as more addresses from the reserved range are allocated to hosts on the local link the number of collisions necessarily increases as well which degrades overall performance. Products such as QIP meet this need in the enterprise.

This standard is widely implemented in most major operating systems, most of which "more or less" adhere to this specification. While I have remained true to the specification and to the algorithms detailed therein I have in some ways made "enhancements"; one example being my pseudorandom address selection will generate link-local addresses in blocks of ten. This is similar to the implementation found in OS X and some of the various offerings by Microsoft. This decision was simply a matter of convenience and nothing more.

This module, LinkLocal::IPv4::Interface provides the main entry point into this implementation. Because the specification recommends that link-local address are generated in a pseudorandom fashion using something unique to the particular host on which they are being generated such as a MAC address, I have by design coupled the selection of addresses closely with the interface object itself; given that I am indeed using the interface hardware MAC as a seed to srand() this just made good sense to me. The primary gateway into this process is the call to the if_config() method. This method will step through the various steps in the address selection process and will configure the interface with a fully compliant IPv4 link-local address upon completion.

There are some things I would like to note here. First, this implementation makes absolutely no assumptions about the current state of the interface at any time. Client code should know this. The specification is quite clear that IPv4 link-local addresses are to be used only in the absence of a fully routable IPv4 address. The dynamic configuration of an IPv4 link-local address is to never interfere with the operation of any of the other processes whereby a host can acquire a standard, routable address such as a DHCP state machine or static assignments under the direction of a network administrator. This implementation is only to be used at such a time that a determination has been made that there are no operable and routable addresses configured on the interface. This library does not at any time make any assumptions about the operability of any addresses assigned to any interfaces on the host, nor does it in any way attempt to determine the management status of any network in which it participates. This is an important point to consider here as small networks have become ubiquitous and "network hopping" with portable devices is certainly a scenario that is much more common today than it was ten or even five years ago. Secondly, the configuration of an IPv4 link-local address is not something which is a static thing; the implementation does not just probe the local physical link for the address, configure the interface and forget about it. At any time an address conflict may occur at which time the selection process may begin again. I have addressed this fact in my design in a broad way. Client code will be expected to register a callback on a hook I provide. Furthermore, I will also expose an optional pure Perl eventing mechanism which can be set to monitor ARP on the local link for any requests or replies which contain the currently configured link-local address. The other option here is that client code may wish to bring its own eventing mechanism to the party. As such I have met both needs by way of Marc Lehmann's AnyEvent module which has been described as the DBI of event loops. For those not familiar with Marc's AnyEvent and Coro material, you might want to run over and check out his stuff. In the world of asynchronous Perl eventing and coroutines, Marc is Master Yoda.

NOTE: This is still very much a work in progress. Much of this is pulled from some old stuff which I had around, including bits and bobs of some UPnP stuff I had in C and which I reimplemented in Perl. As such, some design is happening in situ. In addition to this, I do, unfortunately, have to go to work and feed myself so I am unable to hack on this and other things 24/7. I decided that I would push to CPAN early and chase my crufty push rather than keep it in a git repo on my Mac and constantly pick and preen it and never get anything actually out. So all that said, I will release as quickly and as often as I can and hopefully I will have something here approaching actually useful before long at all, so please bear with me and thanks for your patience.

Also, this is fully intended to work along side such other protocols as Multicast Service Discovery and other lightweight service announcement protocols. The ability to get a valid address usable in communication with other hosts and devices on an unmanaged network is not terribly useful if you cannot find anything out about the particular network in question. As such I am toying with the idea of integrating, albeit very loosely, one or more of the service discovery mechanisms out there as this is what makes link-local addressing actually useful, scenarios such as plugging a laptop and a printer into a network and they just work. While yes, there are full zero configuration suites out there in C and in other languages, there is no lightweight equivalent in Perl.... yet.











The interface attribute contains a reference to the IO::Interface::Simple object type which is instantiated via a Moose type coercion from a string representation of the interface device name. The interface attribute also provides for a number of mappings to the underlying objects methods and attributes by way of the very powerful Moose delegation feature.


The address_list attribute is set to contain a list of ten MAC seeded, pseudorandomly generated IPv4 link-local addresses. As interfaces are checked for collison on the network by way of ARP probes to determine if they are already in use, they are popped off of the list.



This lone constructor takes the name of a network device on the system, as a string and returns a Moose-wrapped IO::Interface::Simple object.



This call returns a string representation of the interface.


Returns the interface index (only valid on BSD-style systems).


Returns a list comprised of all detected interfaces on the system. Note, this will not return a member for the loopback interface.


Returns the string representation of the IPv4 address to which the interface is currently configured. The address is in dotted-decimal notation.


Attempts to set the interface to the IPv4 address string which it takes as its lone parameter. The address must be in dotted-decimal format.


Returns the string representation of the hardware address of the interface. The returned hardware address is in standard colon seperated, hexadecimal digit format.


Returns and pops the next available, pseudo-randomly generated IPv4 link-local address from the attribute list, shrinking that list by one.


General gateway method to this framework. A call to if_config begins the process of dynamically configuring the specified interface with an IPv4 link-local address. This call initiates the process of checking the link-local address cache for the last successfully configured address otherwise a list of ten, new pseudo-random generated addresses is created. The implementation fully adheres to the specification as defined in RFC-3927 as it ARP Probes the first address in the list or from the cache to determine if it is already in use elsewhere on the local link. If it gets no response to its probe packets, it configures the interface with the address and sends ARP Announce packets announcing that it has claimed the address as well as to clear stale ARP cache entries which might exist out on the link. If at any time an ARP packet, request or reply, is detected which contains the address it has selected, it will either concede the address or make a single attempt at address defense, depending upon the context of the packet and its current state.


        PROBE_WAIT          =>  1 second
        PROBE_NUM           =>  3
        PROBE_MIN           =>  1 second
        PROBE_MAX           =>  2 seconds
        ANNOUNCE_WAIT       =>  2 seconds
        ANNOUNCE_NUM        =>  2
        ANNOUNCE_INTERVAL   =>  2 seconds
        MAX_CONFLICTS       => 10
        RATE_LIMIT_INTERVAL => 60 seconds
        DEFEND_INTERVAL     => 10 seconds


Refer to RFC-3927, Dynamic Configuration of IPv4 link-local Adresses, the complete text of which can be found in the top level of the package archive.

perl, IO::Interface::Simple, Moose

This project is also hosted on github at: git@github.com:raymroz/LinkLocal--IPv4.git


What's a bug???


Ray Mroz, <mroz@cpan.org>


Copyright (C) 2010 Ray Mroz

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.