Help needed: cannot send packets larger 230 bytes via vodafone umts

[Rehsack Jens (ext)]

-----Original Message-----
From: Tobias Roth [mailto:roth at iam.unibe.ch] 
Sent: Tuesday, October 11, 2005 4:16 PM
To: Rehsack Jens (ext)
Cc: freebsd-mobile at freebsd.org
Subject: Re: Help needed: cannot send packets larger 230 bytes via
vodafone umts

> On Tue, Oct 11, 2005 at 02:19:42PM +0200, Rehsack Jens (ext) wrote:
> > > > 
> > > > I started some diagnostics why my web wont work, and detected
> > > > that packets larger than 229 byte payload via ping will
swallowed
> > > > by the connection (I don't know where).
> > > 
> > > Did you try traceroute with a packetlength larger than your 229
bytes
> > > to see where the packets get dropped and for what reason?
> > > 
> > > greets, t.
> > 
> > Now I did ;)
> > 
> > And horribly I had to see, that traceroute seems to transport even
> > larger packets an get's the wanted answers. I also tried after that
> > shock >traceroute -P TCP< and seen, that it works, too.
> 
> Initially, my theory was that you have a problem with pathMTU, but I
> am not so sure anymore. If pathMTU is broken, telnetting to port 80
> won't work, since the packets sent have the DF bit set and thus cannot
> be fragmented. When tracerouting with udp or tcp, they don't have that
> bit set, so they get fragmented and things work.
> 
> However, this does not explain why your icmp pings don't get through
> if larger than 229 bytes.
> 
> One last idea: You may try to lower the mtu of your ppp interface
> with ifconfig down to 229 and see if telnet then works. If so, you
> might have an mtu problem after all, if not, something else is rotten.
> 
> good luck, t.

setting net.inet.tcp.path_mtu_discovery=0 didn't change anything, but
# ifconfig tun0 mtu 200
changes something.

Now the DNS lookup wont work anymore, but I get response from my
webserver.
It's really slow, but it is there ;)

And MTU 230 works both - dns & web. Now I think it could be time to look
how to speed up the thing ;)