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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>I think the correct way to set the MTU for
an interface is using ifconfig.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>From the ifconfig manpage:</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
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<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>mtu <i><span style='font-style:italic'>n</span></i></span></font></p>
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<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>Set the maximum transmission unit of the
interface to <i><span style='font-style:italic'>n</span></i>, default is interface
specific. The MTU is used to limit the size of packets that are transmitted
on an interface. Not all interfaces support setting the MTU, and some
interfaces have range restrictions.</span></font></p>
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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Changing the MTU in Windows is a little
bit trickier, as it requires some registry editing (but most network card
drivers let you modify the MTU from their properties page).</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Piero</span></font></p>
<p class=MsoNormal style='margin-left:36.0pt'><font size=2 face=Tahoma><span
lang=EN-US style='font-size:10.0pt;font-family:Tahoma'>-----Original
Message-----<br>
<b><span style='font-weight:bold'>From:</span></b> users-bounces@openswan.org
[mailto:users-bounces@openswan.org] <b><span style='font-weight:bold'>On Behalf
Of </span></b>VRZ (VRZ Koblenz)<br>
<b><span style='font-weight:bold'>Sent:</span></b> </span></font><font size=2 face=Tahoma><span lang=EN-US style='font-size:10.0pt;font-family:Tahoma'>30
March 2005</span></font><font size=2 face=Tahoma><span lang=EN-US
style='font-size:10.0pt;font-family:Tahoma'> </span></font><font
size=2 face=Tahoma><span lang=EN-US style='font-size:10.0pt;font-family:Tahoma'>13:29</span></font><font
size=2 face=Tahoma><span lang=EN-US style='font-size:10.0pt;font-family:Tahoma'><br>
<b><span style='font-weight:bold'>To:</span></b> users@openswan.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> [Openswan Users] (p)mtu
problem between winxp and openswan2.3.0</span></font></p>
<p class=MsoNormal style='margin-left:36.0pt'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p>
<p class=MsoNormal style='margin-right:0cm;margin-bottom:12.0pt;margin-left:
36.0pt'><font size=3 face="Times New Roman"><span lang=DE style='font-size:
12.0pt'>hallo,<br>
<br>
i am using openswan 2.3.0 under suse9.3 (kernel 2.6.10). If i start a
connection from my winxp pro workstation (sp2) via adsl a vpn-connection every
thing works fine until i start a vnc-session. Then the screen is frozen and
nothing works. This is a classical (p)mtu-prohlem as i read but until now i
haven'f found any solution for this problem.<br>
<br>
Here is what i did:<br>
<br>
Under windows xp the largest packet i can ping without defragmentation is 1395
bytes (ping -f -l 1395 xx.xx.xx.xx). The mtu of my linuxbox is 1492 bytes. I am
tuning via iptables the mtu:<br>
<br>
#iptables -A FORWARD -p tcp -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss
1452<br>
iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS
--clamp-mss-to-pmtu<br>
<br>
none of them fixed the problem.<br>
<br>
During the session setup my linux box writes the following message to the
systemlog:<br>
kernel: pmtu discovery on SA ESP/54c693d0/54a99ca9<br>
<br>
Do you have any suggestions?</span></font></p>
<p class=MsoNormal style='margin-left:36.0pt'><font size=3
face="Times New Roman"><span lang=DE style='font-size:12.0pt'><br>
Regards from germany<br>
Frank</span></font></p>
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