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mac-address-rotation.html
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mac-address-rotation.html
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<!DOCTYPE html><html><head><meta charset="utf-8" /><title>MAC address rotation - The Terminal Programmer</title><meta content="2004-03-17T00:00:00-08:00" name="DCTERMS.created" /><meta content="2004-03-17T00:00:00-08:00" name="DCTERMS.modified" /><meta content="Suraj N. Kurapati" name="author" /><meta content="networking, address, dhcp" name="keywords" /><meta content="width=device-width, initial-scale=1" name="viewport" /><meta content="Readably https://github.com/sunaku/readably" name="generator" /><link href="style.css" rel="stylesheet" type="text/css" /><link href="index.atom" rel="alternate" title="feed" type="application/atom+xml" /><script src="js/jquery.slim.min.js"></script></head><body><article data-entry-id="mac-address-rotation" id="body"><header><div class="navigation"><a class="rootlink" href="index.html#mac-address-rotation" title="The Terminal Programmer"><span>The Terminal Programmer</span></a></div><h1 class="title">MAC address rotation</h1><div class="author">Suraj N. Kurapati</div><time class="date" datetime="2004-03-17T00:00:00-08:00">17 March 2004</time></header><hr /><div class="description"></div><div class="content"><ol class="table-of-contents"><li><a id="__problem__" href="#problem" class="downlink">Problem</a><ol></ol></li><li><a id="__approach__" href="#approach" class="downlink">Approach</a><ol></ol></li><li><a id="__solution__" href="#solution" class="downlink">Solution</a><ol></ol></li></ol><p>MAC (Media Access Control) addresses are globally unique host (any network
entity capable of sending and receiving data) identifiers used at the Data-
Link layer of the OSI (Open Systems Interconnect) network model. By their very
nature, they provide a mechanism for implementing network access policies by
ISP (Internet Service Provider)s, such as allowing or restricting access to
any hosts of their choosing.</p>
<div id="problem" class="section"></div><h1 class="heading">Problem<a href="#problem" class="permalink" title="Permalink"></a><a href="#__problem__" class="uplink" title="Contents"></a></h1>
<p>Consider an ISP which denies network access to certain hosts by adding their
MAC addresses to a denied-list within the ISP’s DHCP (Dynamic Host
Configuration Protocol) server.</p>
<div id="approach" class="section"></div><h1 class="heading">Approach<a href="#approach" class="permalink" title="Permalink"></a><a href="#__approach__" class="uplink" title="Contents"></a></h1>
<p>Fortunately, a host whose MAC address is listed in the denied-list can emulate
a different MAC address and fool the ISP’s DHCP server and regain network
access.</p>
<p>Note that MAC address emulation is a feasible alternative to the near
impossible task of altering the actual MAC address (which is hard-coded into
the SRAM (Static Random Access Memory) of NIC (Network Interface Controller)s
by manufacturers.</p>
<div id="solution" class="section"></div><h1 class="heading">Solution<a href="#solution" class="permalink" title="Permalink"></a><a href="#__solution__" class="uplink" title="Contents"></a></h1>
<p>There exist many software tools for emulating MAC addresses, including
<code>ifconfig</code> for GNU/Linux and <a href="http://www.klcconsulting.net/smac/">SMAC</a> for
Microsoft Windows.</p>
<p>For ISPs who deny network access when, say, a bandwidth limit is exceeded,
hosts can maintain nearly constant (there is a short down-time during each
rotation) network access by scheduling changes or <em>rotations</em> in their
emulated MAC address. During rotations, a new MAC address can be assembled
using any valid 6-digit <a href="http://standards.ieee.org/regauth/oui/">OUI (Organization Unique Identifier)
prefix</a> followed by any 6-digit
hexadecimal number.</p>
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