linux-kernel - Re: mss to pmtu clamping partially broken?

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Message-ID: <20070702182850.GB14507@ipom.com>
Date:	Mon, 2 Jul 2007 11:28:50 -0700
From:	Phil Dibowitz <phil@...m.com>
To:	Andreas Steinmetz <ast@...dv.de>
Cc:	Jan Engelhardt <jengelh@...putergmbh.de>,
	netfilter-devel@...ts.netfilter.org,
	Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>
Subject: Re: mss to pmtu clamping partially broken?

On Mon, Jul 02, 2007 at 07:04:12PM +0200, Andreas Steinmetz wrote:
> Jan Engelhardt wrote:
> > Do you really need clamping? It's a hack, since TCP should do MSS negotiation
> > itself. (Of course it may happen that some routers are broken.) But usually not
> > for incoming packets.
> 
> You never know when you hit ICMP blackholes, broken routers and other
> evil things. Better safe than sorry so clamping is the way to go for me.

I encourage you to report PMTUD Blackholes to the MSS Initiative at
http://www.phildev.net/mss/

We'll notify them, and if we can't get them to fix it, blacklist them. We have
more fixed sites than blacklisted sites, so it's at least somewhat successful.

-- 
Phil Dibowitz                             phil@...m.com
Open Source software and tech docs        Insanity Palace of Metallica
http://www.phildev.net/                   http://www.ipom.com/

"Never write it in C if you can do it in 'awk';
 Never do it in 'awk' if 'sed' can handle it;
 Never use 'sed' when 'tr' can do the job;
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 Avoid using 'cat' whenever possible" -- Taylor's Laws of Programming


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