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	Comments on: Unauthorized DHCP Servers: DENIED!	</title>
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	<description>David Szpunar: Owner, Servant 42 and Servant Voice</description>
	<lastBuildDate>Tue, 13 Dec 2011 02:22:27 +0000</lastBuildDate>
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		<title>
		By: David Szpunar		</title>
		<link>/2009/09/08/unauthorized-dhcp-servers-denied/comment-page-1/#comment-17075</link>

		<dc:creator><![CDATA[David Szpunar]]></dc:creator>
		<pubDate>Tue, 13 Dec 2011 02:22:27 +0000</pubDate>
		<guid isPermaLink="false">http://infotech.davidszpunar.com/?p=395#comment-17075</guid>

					<description><![CDATA[In reply to &lt;a href=&quot;/2009/09/08/unauthorized-dhcp-servers-denied/comment-page-1/#comment-17068&quot;&gt;Anatoliy Lisovskiy&lt;/a&gt;.

That comment seems a bit jumbled, but yes I have found it frustrating when something is written for Internet Explorer and subsequent versions of IE don&#039;t work. Switch firmware is not immune from this. Fortunately, better companies&#039; newer products seem to be coming with much more cross-browser compatibility (especially as the last several releases of browsers gain more dynamic features and are a little more standardized in how they are implemented) which also tends to fix the &quot;new browser doesn&#039;t work&quot; issue as a nice little side-effect.

Doesn&#039;t help the old stuff that&#039;s still poorly-written of course. But eventually (and in some churches, eventually is a long time!) this gear will be obsolete and will be replaced. It is a slow cycle.]]></description>
			<content:encoded><![CDATA[<p>In reply to <a href="/2009/09/08/unauthorized-dhcp-servers-denied/comment-page-1/#comment-17068">Anatoliy Lisovskiy</a>.</p>
<p>That comment seems a bit jumbled, but yes I have found it frustrating when something is written for Internet Explorer and subsequent versions of IE don&#8217;t work. Switch firmware is not immune from this. Fortunately, better companies&#8217; newer products seem to be coming with much more cross-browser compatibility (especially as the last several releases of browsers gain more dynamic features and are a little more standardized in how they are implemented) which also tends to fix the &#8220;new browser doesn&#8217;t work&#8221; issue as a nice little side-effect.</p>
<p>Doesn&#8217;t help the old stuff that&#8217;s still poorly-written of course. But eventually (and in some churches, eventually is a long time!) this gear will be obsolete and will be replaced. It is a slow cycle.</p>
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		<title>
		By: Anatoliy Lisovskiy		</title>
		<link>/2009/09/08/unauthorized-dhcp-servers-denied/comment-page-1/#comment-17068</link>

		<dc:creator><![CDATA[Anatoliy Lisovskiy]]></dc:creator>
		<pubDate>Fri, 04 Nov 2011 03:56:27 +0000</pubDate>
		<guid isPermaLink="false">http://infotech.davidszpunar.com/?p=395#comment-17068</guid>

					<description><![CDATA[When switches do something they should not do they don&#039;t do properly what normal switches must do. They are no more switches, but not yet neither routers, nor firewalls. 

I mean all that HP strategy called &quot;Fix problems&quot; instead of &quot;Go for the goal&quot;. HP and Microsoft in technical terms are very alike, they both go for money fixing problems. Instead of getting money offering better designed and implemented products. As the result, for example, HP management software can&#039;t run on Microsoft OS because HP did not expect Microsoft to fix new bugs in IE making HP Insight Manager incompatible.

It is bad solution when some problem created by messy network planning is &quot;fixed&quot; by the device that is not supposed to deal with such problems. 

Anyway, thank you for the article, now we know what to do if some switch stops switching...]]></description>
			<content:encoded><![CDATA[<p>When switches do something they should not do they don&#8217;t do properly what normal switches must do. They are no more switches, but not yet neither routers, nor firewalls. </p>
<p>I mean all that HP strategy called &#8220;Fix problems&#8221; instead of &#8220;Go for the goal&#8221;. HP and Microsoft in technical terms are very alike, they both go for money fixing problems. Instead of getting money offering better designed and implemented products. As the result, for example, HP management software can&#8217;t run on Microsoft OS because HP did not expect Microsoft to fix new bugs in IE making HP Insight Manager incompatible.</p>
<p>It is bad solution when some problem created by messy network planning is &#8220;fixed&#8221; by the device that is not supposed to deal with such problems. </p>
<p>Anyway, thank you for the article, now we know what to do if some switch stops switching&#8230;</p>
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		<item>
		<title>
		By: David Szpunar		</title>
		<link>/2009/09/08/unauthorized-dhcp-servers-denied/comment-page-1/#comment-15868</link>

		<dc:creator><![CDATA[David Szpunar]]></dc:creator>
		<pubDate>Mon, 13 Sep 2010 05:25:21 +0000</pubDate>
		<guid isPermaLink="false">http://infotech.davidszpunar.com/?p=395#comment-15868</guid>

					<description><![CDATA[In reply to &lt;a href=&quot;/2009/09/08/unauthorized-dhcp-servers-denied/comment-page-1/#comment-15860&quot;&gt;Michael Newton&lt;/a&gt;.

Thanks Michael, that is a good idea, especially in an environment where there is no peer-to-peer connectivity required beyond server access. It would certainly be even more secure than just blocking DHCP. However, my guess is that in a church environment, or at least many I&#039;ve seen, there are enough exceptions where users share directly computer-to-computer that it may not be the best solution for everyone. However, some Church IT folks are looking for ways to limit the often non-authorized direct-sharing, so perhaps server-only access could be a boon as well! I never really thought of using it, but there are a good number of systems I can think of that wouldn&#039;t need access to anything but the uplink port...if I have some spare time I may examine this a bit more myself. Thanks again!]]></description>
			<content:encoded><![CDATA[<p>In reply to <a href="/2009/09/08/unauthorized-dhcp-servers-denied/comment-page-1/#comment-15860">Michael Newton</a>.</p>
<p>Thanks Michael, that is a good idea, especially in an environment where there is no peer-to-peer connectivity required beyond server access. It would certainly be even more secure than just blocking DHCP. However, my guess is that in a church environment, or at least many I&#8217;ve seen, there are enough exceptions where users share directly computer-to-computer that it may not be the best solution for everyone. However, some Church IT folks are looking for ways to limit the often non-authorized direct-sharing, so perhaps server-only access could be a boon as well! I never really thought of using it, but there are a good number of systems I can think of that wouldn&#8217;t need access to anything but the uplink port&#8230;if I have some spare time I may examine this a bit more myself. Thanks again!</p>
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		<title>
		By: Michael Newton		</title>
		<link>/2009/09/08/unauthorized-dhcp-servers-denied/comment-page-1/#comment-15860</link>

		<dc:creator><![CDATA[Michael Newton]]></dc:creator>
		<pubDate>Thu, 02 Sep 2010 15:01:17 +0000</pubDate>
		<guid isPermaLink="false">http://infotech.davidszpunar.com/?p=395#comment-15860</guid>

					<description><![CDATA[You can also use source port filtering (2600, 2610), protected ports (2510, 2520), or port isolation (2500) to prevent user ports from communicating with anything but the uplink port. This also stops rogue DHCP servers and works on L2 switches.

(Note port isolation doesn&#039;t work with VLANs.)]]></description>
			<content:encoded><![CDATA[<p>You can also use source port filtering (2600, 2610), protected ports (2510, 2520), or port isolation (2500) to prevent user ports from communicating with anything but the uplink port. This also stops rogue DHCP servers and works on L2 switches.</p>
<p>(Note port isolation doesn&#8217;t work with VLANs.)</p>
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		<title>
		By: David Szpunar		</title>
		<link>/2009/09/08/unauthorized-dhcp-servers-denied/comment-page-1/#comment-14976</link>

		<dc:creator><![CDATA[David Szpunar]]></dc:creator>
		<pubDate>Tue, 22 Sep 2009 21:57:31 +0000</pubDate>
		<guid isPermaLink="false">http://infotech.davidszpunar.com/?p=395#comment-14976</guid>

					<description><![CDATA[In reply to &lt;a href=&quot;/2009/09/08/unauthorized-dhcp-servers-denied/comment-page-1/#comment-14942&quot;&gt;Jeremy good&lt;/a&gt;.

Thanks for the additional details Jeremy!]]></description>
			<content:encoded><![CDATA[<p>In reply to <a href="/2009/09/08/unauthorized-dhcp-servers-denied/comment-page-1/#comment-14942">Jeremy good</a>.</p>
<p>Thanks for the additional details Jeremy!</p>
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		<item>
		<title>
		By: Jeremy good		</title>
		<link>/2009/09/08/unauthorized-dhcp-servers-denied/comment-page-1/#comment-14942</link>

		<dc:creator><![CDATA[Jeremy good]]></dc:creator>
		<pubDate>Tue, 08 Sep 2009 19:51:08 +0000</pubDate>
		<guid isPermaLink="false">http://infotech.davidszpunar.com/?p=395#comment-14942</guid>

					<description><![CDATA[Great detailed post! You can also set an ACL on the ports or vlans to prohibit dhcp traffic from other dhcp servers or devices with IP addresses different than your vlan IP address range. In some cases this might be easier. Also having proper vlan segregation helps a lot.]]></description>
			<content:encoded><![CDATA[<p>Great detailed post! You can also set an ACL on the ports or vlans to prohibit dhcp traffic from other dhcp servers or devices with IP addresses different than your vlan IP address range. In some cases this might be easier. Also having proper vlan segregation helps a lot.</p>
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