mss to pmtu clamping partially broken?

Phil Dibowitz phil at ipom.com
Mon Jul 2 20:28:50 CEST 2007


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 at ipom.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;
 Never invoke 'tr' when 'cat' is sufficient;
 Avoid using 'cat' whenever possible" -- Taylor's Laws of Programming

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