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List:       linux-kernel
Subject:    Re: path MTU bug still there?
From:       Jussi Hamalainen <count () theblah ! org>
Date:       2000-12-31 15:28:05
[Download RAW message or body]

On Sun, 31 Dec 2000, Mikael Abrahamsson wrote:

> When the linux box does TCP to the outside it'll use the MTU of
> the tunnel (default route is the tunnel) and thus works perfectly
> (since TCP MSS will be set low enough to fit into the tunnel).

In my case I can't access a problematic host even from the router
box.

> Could it be some kind of incompability at the tunnel level that
> make you unable to receive large packets over the tunnel?

Could be. The internet connection is a 64k ISDN link.

> Have you tcpdump:ed to see if the tunnel packets actually make it
> the way they should?

I can't snoop the actual tunnel device, because tcpdump and sniffit
give me an unknown media type error. Here's a tcpdump from the router
box's ethernet device of a HTTP session (using lynx) to
www.doomworld.com:

17:19:46.126297 xxx.xxx.xxx.xxx.1029 > 206.96.221.6.80: S 2549095564:2549095564(0) win 32120 <mss \
                1460,sackOK,timestamp 649398[|tcp]> (DF)
17:19:46.386142 206.96.221.6.80 > xxx.xxx.xxx.xxx.1029: S 1631828281:1631828281(0) ack 2549095565 win \
                30660 <mss 1460,sackOK,timestamp 91687185[|tcp]> (DF)
17:19:46.386142 206.96.221.6.80 > xxx.xxx.xxx.xxx.1029: S 1631828281:1631828281(0) ack 2549095565 win \
                30660 <mss 1460,sackOK,timestamp 91687185[|tcp]> (DF)
17:19:46.386142 xxx.xxx.xxx.xxx.1029 > 206.96.221.6.80: . ack 1 win 32120 <nop,nop,timestamp 649423 \
                91687185> (DF)
17:19:46.386142 xxx.xxx.xxx.xxx.1029 > 206.96.221.6.80: P 1:369(368) ack 1 win 32120 <nop,nop,timestamp \
                649423 91687185> (DF)
17:19:46.685963 206.96.221.6.80 > xxx.xxx.xxx.xxx.1029: . ack 369 win 30660 <nop,nop,timestamp 91687216 \
                649423> (DF)
17:19:46.685963 206.96.221.6.80 > xxx.xxx.xxx.xxx.1029: . ack 369 win 30660 <nop,nop,timestamp 91687216 \
649423> (DF)

And the connection locks up. This happens every time. I don't have
access to the Cisco so I can't dump traffic on the remote end of
my tunnel.

-- 
-=[ Count Zero / TBH - Jussi Hämäläinen - email count@theblah.org ]=-

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