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<tt>CentOS release 5.6 (Final)<br>
Linux Openswan U2.6.33/K2.6.18-238.12.1.el5 (netkey)<br>
xl2tpd version: xl2tpd-1.2.6<br>
<br>
Hi,<br>
<br>
I have a set-up with several Windows (XP, Windows 7) roadwarriors
connecting via L2TP/IPsec VPN. All works fine until a few days
ago. Some users can still connect but it seems packets are getting
fragmented disallowing access to some services on the VPN (e.g.
some samba shares, POP mail accounts via Outlook).<br>
<br>
Part of my debugging problem is the roadwarriors use all kinds of
different service providers to connect (3G USB modems, 3G Mobiles,
Home internet plans, Hotel wifi, etc...).<br>
<br>
I have set some client registry settings to do PMTU and PMTU Black
Hole detection. O</tt><tt>n the server I </tt><tt>have enabled
ICMP and also set net.ipv4.tcp_mtu_probing = 1<br>
<br>
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\EnablePMTUBHDetect
= 1<br>
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\</tt><tt>EnablePMTUDiscovery
= 1<br>
<br>
options.xl2tpd had mtu 1372 and mru 1372.<br>
<br>
On the Windows client I see the VPN interface MTU being set to
1372 (using c:\> netsh interface ipv4 show interfaces)<br>
<br>
When I lower the mtu and mru to 1280 many of the issues went away
but I still see some fragmentation. The client reflects that
change in it's VPN MTU also being set to 1280.<br>
<br>
My questions are: </tt><tt>What is the recommended setting and </tt><tt>can
I go any lower? Is there any other issue I'm overlooking. Config
files provided on request.<br>
<br>
Regards<br>
<br>
</tt>
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<pre class="moz-signature" cols="72">Tom Robinson
System Administrator
<img alt="MoTeC" src="cid:part1.08030603.09060409@motec.com.au" height="49" width="144">
121 Merrindale Drive
Croydon South
3136 Victoria
Australia
T: +61 3 9761 5050
F: +61 3 9761 5051
E: <a class="moz-txt-link-abbreviated" href="mailto:tom.robinson@motec.com.au">tom.robinson@motec.com.au</a></pre>
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