Subject: Re: IP NAT problem over pppoe(4)
To: None <tech-net@netbsd.org>
From: Matthias Scheler <tron@zhadum.de>
List: tech-net
Date: 12/11/2002 18:21:24
In article <20021210103723.GA26542@colwyn.zhadum.de>,
> after changing the Internet provider for my DSL line I experience
> strange connectivity problems on TCP connections of a NetBSD system
> behind my NetBSD IP NAT gateway.
> 
> The affected IP NAT client can download and upload files via "scp"
> from and to other systems on the Internet without problems. The
> trouble starts if I try to access "cvs.netbsd.org":
> 
> a) The IP NAT gateway can upload files to and download files from
>    "cvs.netbsd.org" via "scp" without problems.
> b) The IP NAT client can upload files to "cvs.netbsd.org" with "scp"
>    but always gets stuck while downloading files.

I've found the problem: the provider wants to use a MTU of 1460 and
not 1492 on the DSL connection. pppoe(4) accepts that value during
the PPP negotiation but doesn't use it afterwards.

After setting the MTU to 1460 manually and reducing MSS clamp to
1408 - 1420 should do in theory but doesn't in reality - everything
works fine again.

	Kind regards

-- 
Matthias Scheler                                  http://scheler.de/~matthias/