<br><tt><font size=2>Arnaud Fenioux <afenioux@gmail.com> wrote on
31/12/2010 10:00:45:<br>
> >> Right, the mtu given by the 3G link is equal to 1486<br>
[SNIP]</font></tt>
<br><tt><font size=2>> ifconfig is fine.<br>
> but a "ping -s XXX -M do" with XXX > 548 (576 with the
headers),<br>
> hasn't any answer,<br>
</font></tt>
<br><tt><font size=2>Pinging the Nx server may we presume ???</font></tt>
<br>
<br><tt><font size=2>> although I can see much bigger packets when I
dumping while browsing...<br>
[SNIP]</font></tt>
<br><tt><font size=2>> I mean, it worked for windows, not for Linux
event if I set the mtu to 1500<br>
> ><br>
> >> why did it worked with previous version of ubuntu ( 9.10-
server-side<br>
> >> speaking) ?<br>
</font></tt>
<br><tt><font size=2>Something has changed somewhere !! Lets have a look.</font></tt>
<br>
<br><tt><font size=2>> > Sounds like something isn't letting ICMP
through, so it is defaulting to<br>
> > 1500, and/or something just isn't working, like the 3G driver
on 10.04<br>
> > thinks it should be set to 1500 when the link provided is actually
lower.<br>
> ><br>
> > Try putting the server back up to 1500 and setting the 3G interface<br>
> > to something lower.<br>
> <br>
> I tried severals values on the 3G interface (500-1500), nothing worked,<br>
> the reason could be because I'm NATed/Proxyfied by my ISP...<br>
> I'm using a 10.x.x.x IP on a "point to point noarp multicast"
link<br>
</font></tt>
<br><tt><font size=2>That's not the issue else the windows connection to
NX wouldn't work.</font></tt>
<br>
<br><tt><font size=2>I'd say that two things are broken.</font></tt>
<br>
<br><tt><font size=2>1/ The 3G linux driver is not setting the MTU (it
does in windows</font></tt>
<br><tt><font size=2> so PMTUD isn't
needed)</font></tt>
<br>
<br><tt><font size=2>2/ The NX server is not getting ICMP, so it won't
get pings, nor</font></tt>
<br><tt><font size=2>will it get PMTUD (I doubt only Type3-C4 packets are
filtered).</font></tt>
<br>
<br><tt><font size=2>So, on the NX server run your favourite tcpdump :-</font></tt>
<br><tt><font size=2> (sudo) tcpdump
-vv icmp</font></tt>
<br><tt><font size=2>then</font></tt>
<br><tt><font size=2> ping the NX server
from :-</font></tt>
<br><tt><font size=2> your 3G </font></tt>
<br><tt><font size=2> your remote ADSL
and</font></tt>
<br><tt><font size=2> the NX-server
segment</font></tt>
<br>
<br><tt><font size=2>This should help spot any ICMP filtering.</font></tt>
<br>
<br><tt><font size=2>Then leaving tcpdump running:-</font></tt>
<br><tt><font size=2> connect an NX
session</font></tt>
<br><tt><font size=2>watch for "Frag needed and DF set" as the
session connects</font></tt>
<br><tt><font size=2>and see what sends them.</font></tt>
<br>
<br><tt><font size=2>I predict you won't see any, because something is
filtering them</font></tt>
<br><tt><font size=2>out until you find and remove the filtering.</font></tt>
<br><tt><font size=2>So</font></tt>
<br><tt><font size=2>Do you run a firewall on the 10.04 server</font></tt>
<br><tt><font size=2>or</font></tt>
<br><tt><font size=2>do you have ICMP disabled on the edge router at the
NX</font></tt>
<br><tt><font size=2>site</font></tt>
<br><tt><font size=2>(maybe 9.04 does something different from 10.04 -
like not having</font></tt>
<br><tt><font size=2>a bug in PMTUD or maybe even not having PMTUD switched</font></tt>
<br><tt><font size=2>off as a default (unlikely), or maybe 9.04 automatically
reduces</font></tt>
<br><tt><font size=2>the MTU if connections get interrupted, without waiting
for ICMP</font></tt>
<br><tt><font size=2>to tell it that it needs to)</font></tt>
<br>
<br><tt><font size=2>> <br>
> Well, happy new year!<br>
</font></tt>
<br><tt><font size=2>And to you too !!</font></tt>
<br>
<br><tt><font size=2>> and BTW, do you have an idea, why 3.4.0 backend
is (really) slower<br>
> than the 3.3.0 (even in ADSL) to establish the display connection?
;)<br>
</font></tt>
<br><tt><font size=2>I haven't noticed this difference. Check to see where
your delay is</font></tt>
<br><tt><font size=2>occuring.</font></tt>
<br><tt><font size=2>Is it part of the NX ssh connection (eg sshd dns reverse
lookups) or</font></tt>
<br><tt><font size=2>is it after the ssh connection is in place, at agent
startup ??</font></tt>
<br>
<br>