[FreeNX-kNX] Re: Connection error with ubuntu 10.04 & 10.10

[chris at ccburton.com]

Arnaud Fenioux <afenioux at gmail.com> wrote on 30/12/2010 17:37:19:

> On Thu, Dec 30, 2010 at 4:31 PM,  <chris at ccburton.com> wrote:
> [SNIP]
> >
> > Did you check out MTU over the 3G link.
> >
> > There should be no difference whichever way it gets there, but
> > a session which partially starts and then falls over with the server
> > complaining about losing the client is one (good) symptom of
> > path-MTU not working.
> >
> > I guess you know how to check this out from reading your posts.
> 
> Right, the mtu given by the 3G link is equal to 1486

Due to their back haul tagging probably, unless they use ATM
in which case they like 1478 (or something) 

> (checked with an ifconfig and some tests like "ping google.com -s 
> 1500 -M do" )

or even "ifconfig" or do you mean the link is actually lower MTU
than the driver thinks it is ???

> I tried to set this value higher on the client interface, but it 
> didn't worked,
> since I set the mtu to a lower value on the server interface, it's
> working like a charm :)

I am charming (so I say)
 
> Questions are : why are the packet set with the flag "don't frangment"

Security and performance, not necessarily in that order.

> (I checked with a tcpdump -vv) is that something due to ssh?

If you have routers fragmenting all packets, they tend not to be
doing much else!!
so we "all" use path-mtu discovery now, (if we can get ICMP through
the firewall)

Sometimes the session start up uses only smaller packets,
and the session only moves up to larger ones as more traffic flows,
so you get so far and the higher level protocols time out with a
guess-error message.

> why is windows mtu set to 1500? (command "netsh interface ipv4 show
> interfaces") something due to the driver?

That's the default. Did you mean to ask that ??

> why did it worked with previous version of ubuntu ( 9.10-  server-side
> speaking) ?

Sounds like something isn't letting ICMP through, so it is defaulting to
1500, and/or something just isn't working, like the 3G driver on 10.04
thinks it should be set to 1500 when the link provided is actually lower.

Try putting the server back up to 1500 and setting the 3G interface
to something lower.

> 
> We may not find the answers, I let them as a reflexion to the readers...

They'll love you for that !!

> 
> Cheers,
> and THANK YOU for your help

Good luck etc etc.
Keep learning (if not teaching)



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