[39599] in North American Network Operators' Group
Re: PPPOE, MTU, and boom.
daemon@ATHENA.MIT.EDU (Simon Lockhart)
Wed Jul 18 02:53:51 2001
To: Alex Rubenstein <alex@nac.net>
Cc: nanog@nanog.org
In-Reply-To: Your message of "Wed, 18 Jul 2001 02:50:19 EDT."
<Pine.WNT.4.33.0107180244240.1064-100000@neon>
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Date: Wed, 18 Jul 2001 07:53:09 +0100
Message-Id: <28162.995439189@sunf25>
From: Simon Lockhart <simonl@rd.bbc.co.uk>
Errors-To: owner-nanog-outgoing@merit.edu
>I have confirmed that when I block all ICMP to/from a website, we cannot
>browse that site -- which is somewhat obivious. The question is, how, as
>an internet community as a whole, do we fix this?
>
>Seems to me that most people using PPPOE would have a problem here. Or, am
>I alone?
>
>My testing has been limited to Win2k, but I've heard similar reports on
>WinME, 98, etc.
We've come across this too, and spent quite a while diagnosing. The
problem exists wherever there's an MTU reduction, and is caused by a
combination of ICMP filtering (breaks PMTUD), and Microsoft's attempt at
PMTUD (they just set the DF bit on all packets and expect to get an ICMP
reply back if the packet is too large).
Simon
--
Simon Lockhart | Tel: +44 (0)1737 839676
Internet Engineering Manager | Fax: +44 (0)1737 839516
BBC Internet Services | Email: Simon.Lockhart@bbc.co.uk
Kingswood Warren,Tadworth,Surrey,UK | URL: http://support.bbc.co.uk/
