Date: Sun, 07 Jan 2001 10:03:16 -0800 From: Michael Wozniak <mwozniak@netcom.ca> To: doc@FreeBSD.org Subject: update to "Chapter 10. PPP" of "Frequently Asked Questions for FreeBSD 2.X, 3.X and 4.X" Message-ID: <002301c078d4$1f1a6fc0$0a80a8c0@mwozniak.uniservers.com>
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[-- Attachment #1 --] Hi, you have quoted me in the FAQ reproduced below. I would like to add to the statement "the Telco router is not sending ICMP ``must fragment'' back to the www site you are trying to load" that sometimes the Telco _is_ sendind a "must fragment" back to the www site but the firewall at the www site is dropping it (also a misconfiguration.) Also, somebody reading this FAQ asked me about Win2K so I referred them to Microsoft Knowledge Base article "Q120642 - TCP/IP & NBT Configuration Parameters for Windows NT and Windows 2000" It indicated that the registry key has changed to Tcpip\Parameters\Interfaces\<ID for Adapter>\MTU Lastly, if you could change the reference "MS KB" to "Microsoft Knowledge Base" with a link to http://search.support.microsoft.com/kb, that would help some people figure these things out on their own. Thanks, Mike 10.27. Why do MacOS and Windows 98 connections freeze when running PPPoE on the gateway Thanks to Michael Wozniak <mwozniak@netcom.ca> for figuring this out and Dan Flemming <danflemming@mac.com> for the Mac solution: This is due to what's called a ``Black Hole'' router. MacOS and Windows 98 (and maybe other Microsoft OSs) send TCP packets with a requested segment size too big to fit into a PPPoE frame (MTU is 1500 by default for ethernet) and have the ``don't fragment'' bit set (default of TCP) and the Telco router is not sending ICMP ``must fragment'' back to the www site you are trying to load. When the www server is sending you frames that don't fit into the PPPoE pipe the Telco router drops them on the floor and your page doesn't load (some pages/graphics do as they are smaller than a MSS.) This seems to be the default of most Telco PPPoE configurations (if only they knew how to program a router... sigh...) One fix is to use regedit on your 95/98 boxes to add the following registry entry... HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Class\NetTrans\0000\Max MTU It should be a string with a value ``1450'' (more accurately it should be ``1464'' to fit TCP packets into a PPPoE frame perfectly but the ``1450'' gives you a margin of error for other IP protocols you may encounter). Refer to MS KB # ``Q158474 - Windows TCPIP Registry Entries'' and ``Q120642 - TCPIP & NBT Configuration Parameters for Windows NT '' for more information on changing Windoze MTU to work with a FreeBSD/NAT/PPPoE router. [-- Attachment #2 --] <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> <TITLE></TITLE> <META content="MSHTML 5.00.2722.2800" name=GENERATOR></HEAD> <BODY bgColor=#ffffff> <DIV><FONT face=Arial size=2>Hi, you have quoted me in the FAQ reproduced below. </FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>I would like to add to the statement</FONT><FONT face=Arial size=2> "the Telco router is not sending ICMP ``must fragment''</FONT></DIV> <DIV><FONT face=Arial size=2>back to the www site you are trying to load" </FONT><FONT face=Arial size=2>that sometimes the Telco _is_ sendind a "must</FONT></DIV> <DIV><FONT face=Arial size=2>fragment" back to the www site but the firewall at the www si</FONT><FONT face=Arial size=2>te is dropping it (also a misconfigur</FONT><FONT face=Arial size=2>ation.)</FONT></DIV> <DIV> </DIV> <DIV><FONT face=Arial size=2>Also, somebody reading this FAQ asked me about Win2K so I referred them to Microsoft</FONT></DIV> <DIV><FONT face=Arial size=2>Knowledge Base article "<FONT face="Verdana, Arial, Helvetica" size=2><A href="http://support.microsoft.com/support/kb/articles/Q120/6/42.asp?LN=EN-US&SD=gn&FR=0&qry=mtu&rnk=1&src=DHCS_MSPSS_gn_SRCH&SPR=WIN2000"><STRONG>Q120642 - TCP/IP & NBT Configuration Parameters for Windows NT and Windows 2000</STRONG></A><FONT face=Arial>"</FONT></FONT></FONT></DIV> <DIV><FONT face=Arial size=2>It indicated that the registry key has changed to Tcpip\Parameters\Interfaces\<ID for Adapter>\MTU</FONT></DIV> <DIV> </DIV> <DIV><FONT face=Arial size=2>Lastly, if you could change the reference "MS KB" to "Microsoft Knowledge Base" with a link</FONT></DIV> <DIV><FONT face=Arial size=2>to <A href="http://search.support.microsoft.com/kb">http://search.support.microsoft.com/kb</A>, that would help some people figure these things out on their</FONT></DIV> <DIV><FONT face=Arial size=2>own.</FONT></DIV> <DIV> </DIV> <DIV><FONT face=Arial size=2>Thanks, Mike</FONT></DIV> <DIV><BR> </DIV> <P><FONT size=2></P> <DIV class=QUESTION> <P><BIG><A name=MACOS-WIN98-PPPOE-FREEZE></A><B>10.27. Why do MacOS and Windows 98 connections freeze when running PPPoE on the gateway</B></BIG></P></DIV> <DIV class=ANSWER> <P><B></B>Thanks to Michael Wozniak <TT class=EMAIL><<A href="mailto:mwozniak@netcom.ca">mwozniak@netcom.ca</A>></TT> for figuring this out and Dan Flemming <TT class=EMAIL><<A href="mailto:danflemming@mac.com">danflemming@mac.com</A>></TT> for the Mac solution:</P> <P>This is due to what's called a ``Black Hole'' router. MacOS and Windows 98 (and maybe other Microsoft OSs) send TCP packets with a requested segment size too big to fit into a PPPoE frame (MTU is 1500 by default for ethernet) <I class=EMPHASIS>and</I> have the ``don't fragment'' bit set (default of TCP) and the Telco router is not sending ICMP ``must fragment'' back to the www site you are trying to load. When the www server is sending you frames that don't fit into the PPPoE pipe the Telco router drops them on the floor and your page doesn't load (some pages/graphics do as they are smaller than a MSS.) This seems to be the default of most Telco PPPoE configurations (if only they knew how to program a router... sigh...)</P> <P>One fix is to use regedit on your 95/98 boxes to add the following registry entry...</P> <P class=LITERALLAYOUT> HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Class\NetTrans\0000\MaxMTU<BR> </P> <P>It should be a string with a value ``1450'' (more accurately it should be ``1464'' to fit TCP packets into a PPPoE frame perfectly but the ``1450'' gives you a margin of error for other IP protocols you may encounter).</P> <P>Refer to MS KB # ``Q158474 - Windows TCPIP Registry Entries'' and ``Q120642 - TCPIP & NBT Configuration Parameters for Windows NT '' for more information on changing Windoze MTU to work with a FreeBSD/NAT/PPPoE router.</P></DIV></FONT></BODY></HTML>help
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