Hoary / kernel 2.6.9: Gaim cannot connect to AIM/ICQ?

[Le grand pinguin]

On Tue, Dec 21, 2004 at 03:58:41PM +0100, Klaus Alexander Seistrup wrote:
> On Tue, 21 Dec 2004 15:19:01 +0100, Le grand pinguin <rm at mh-freiburg.de> wrote:
> 
> >> I've tried
> >>
> >>   # sysctl -w net.ipv4.tcp_window_scaling=0
> >>   # sysctl -w net.ipv4.tcp_timestamps=0
> >>   # sysctl -w net.ipv4.tcp_sack=0
> >>
> >> but that doesn't seem to help.
> >>
> >> Does that mean that the problem is not a TCP Window Scaling problem?
> > 
> > Just out of curiosity: how do you connect to the internet - is there
> > some PPP over ethernet involved? Could this be a plain ol' MTU problem?
> > What does 'ifconfig' say?
> 
> I have a permanent ADSL connection -- the router does the negotiation.
> 
> Ifconfig says:
> 
> eth0      Link encap:Ethernet  HWaddr xx:xx:xx:xx:xx:xx
>           inet addr:x.x.x.x  Bcast:x.x.x.x  Mask:x.x.x.x
>           inet6 addr: x::x:x:x:x/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:690713 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:661966 errors:0 dropped:0 overruns:8 carrier:0
>           collisions:0 txqueuelen:1000
>           RX bytes:241367765 (230.1 MiB)  TX bytes:110451903 (105.3 MiB)
>           Interrupt:19 Base address:0xd400
> 
> MTU is 1500 (and has "always" been, as far as I remember).  If MTU was
> the problem, wouldn't it affect all sites, and not just
> AIM/ICQ/Netscape (and a few others)?

It might be a bit more complicated: if your router does connect to your ADSL
modem with PPP over ethernet the MTU on that segment will be smaller than
the 1500 for ethernet (max ethernet frame size - ppp frame header size which
usually comes dowm to 1492). This is all rather invisible to the end user
as long as path mtu discovery works ... Now, some (stupid?) Websites dissable
ICMP traffic at all and path mtu discovery (which does use ICMP) breaks. You
might end up with a server sending you 1500 size packages with the don't-fragment
bit set that never reach you because the package is to big to get through your
PPPoE segment but can't be fragmented ....
What happens if you manually set your MTU to 1492? A simple 'ifconfig eth0 mtu 1492'
should be enough.

 HTH Ralf Mattes

> Cheers,
> 
> -- 
> Klaus Alexander Seistrup
> SubZeroNet ? Copenhagen ? Denmark
> 
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