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<div class=Section1><pre><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt;color:black'>Does anyone know why this value is being altered by OFED?<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt;color:black'><o:p> </o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt;color:black'>"net.ipv4.tcp_timestamps" is being set to 0 during OFED installation. <o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt;color:black'><o:p> </o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt;color:black'>Default value of this parameter is set to 1 on standard RHEL/SLES distros which OFED installation script modifies to 0. Also, when OFED is uninstalled, it does not reset these sysctl parameters to their original values.<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt;color:black'><o:p> </o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt;color:black'>This parameter is specifically recommended to be turned ON for High performance network. This is a TCP option that can be used to calculate the Round Trip Measurement in a better and more accurate way than the retransmission timeout method can. Accurate value of retransmission timeout should be determined to avoid unnecessary retransmissions and hence to improve TCP performance. RFC 1323 talks about this TCP extension for High Performance. <o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt;color:black'><o:p> </o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt;color:black'>When the parameter net.ipv4.tcp_timestamps=1, then it adds extra 12 bytes into TCP header increasing its size. This has an obvious effect of decrease in bandwidth as we have some extra data flowing. Is this the reason why OFED turns it OFF to net.ipv4.tcp_timestamps=0.<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt;color:black'><o:p> </o:p></span></font></pre>
<p class=MsoNormal><font size=2 color=maroon face="Comic Sans MS"><span
style='font-size:10.0pt;font-family:"Comic Sans MS";color:maroon'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=maroon face="Comic Sans MS"><span
style='font-size:10.0pt;font-family:"Comic Sans MS";color:maroon'><o:p> </o:p></span></font></p>
<p><b><font size=2 color=maroon face=Garamond><span style='font-size:10.0pt;
font-family:Garamond;color:maroon;font-weight:bold'><img width=92 height=55
id="_x0000_i1025" src="cid:image001.jpg@01C9539F.A13A0750" border=0><br>
</span></font></b><strong><b><font size=2 color=maroon face=Garamond><span
style='font-size:10.0pt;font-family:Garamond;color:maroon'>__________________________</span></font></b></strong><b><font
size=2 color=maroon face=Garamond><span style='font-size:10.0pt;font-family:
Garamond;color:maroon;font-weight:bold'><br>
<strong><b><font face=Garamond><span style='font-family:Garamond'>John F. Russo</span></font></b></strong><br>
<strong><b><font face=Garamond><span style='font-family:Garamond'>Manager, Engineering</span></font></b></strong><br>
<strong><b><font face=Garamond><span style='font-family:Garamond'>QLogic
Corporation</span></font></b></strong><br>
<st1:Street w:st="on"><st1:address w:st="on"><strong><b><font face=Garamond><span
style='font-family:Garamond'>780 Fifth Avenue, Suite 140</span></font></b></strong></st1:address></st1:Street><br>
<st1:place w:st="on"><st1:City w:st="on"><strong><b><font face=Garamond><span
style='font-family:Garamond'>King of Prussia</span></font></b></strong></st1:City><strong><b><font
face=Garamond><span style='font-family:Garamond'>, <st1:State w:st="on">PA</st1:State>
<st1:PostalCode w:st="on">19406</st1:PostalCode></span></font></b></strong></st1:place><br>
<strong><b><font face=Garamond><span style='font-family:Garamond'>Direct:
610-233-4866</span></font></b></strong><br>
<st1:place w:st="on"><strong><b><font face=Garamond><span style='font-family:
Garamond'>Main</span></font></b></strong></st1:place><strong><b><font
face=Garamond><span style='font-family:Garamond'>: 610-233-4800</span></font></b></strong><br>
<strong><b><font face=Garamond><span style='font-family:Garamond'>Fax:
610-233-4777</span></font></b></strong><br>
<strong><b><font face=Garamond><span style='font-family:Garamond'>Cell:
610-246-9903</span></font></b></strong><br>
<strong><b><font face=Garamond><span style='font-family:Garamond'>Email: </span></font></b></strong></span></font></b><font
color=maroon><span style='color:maroon'><a href="mailto:John.Russo@qlogic.com"><strong><b><font
size=2 face=Garamond><span style='font-size:10.0pt;font-family:Garamond;
text-decoration:none'>John.Russo@qlogic.com</span></font></b></strong></a><br>
</span></font><font size=2 color=maroon face=Garamond><span style='font-size:
10.0pt;font-family:Garamond;color:maroon'><a href="http://www.qlogic.com"><strong><b><font
face=Garamond><span style='font-family:Garamond;text-decoration:none'>www.qlogic.com</span></font></b></strong></a></span></font><font
color=maroon><span style='color:maroon'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=maroon face="Times New Roman"><span
style='font-size:12.0pt;color:maroon'> <o:p></o:p></span></font></p>
<p class=MsoNormal><strong><b><font size=2 color=maroon face=Garamond><span
style='font-size:10.0pt;font-family:Garamond;color:maroon'>True success is the
undeniable truth that we have proved ourselves.</span></font></b></strong><font
color=maroon><span style='color:maroon'><o:p></o:p></span></font></p>
<p class=MsoNormal><strong><b><i><font size=2 color=maroon face=Garamond><span
style='font-size:10.0pt;font-family:Garamond;color:maroon;font-style:italic'>-Joe
Luppino-Esposito</span></font></i></b></strong><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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