[104357] in North American Network Operators' Group
Re: [NANOG] Microsoft.com PMTUD black hole?
daemon@ATHENA.MIT.EDU (Nathan Anderson/FSR)
Wed May 7 17:48:10 2008
Date: Wed, 07 May 2008 14:47:13 -0700
From: Nathan Anderson/FSR <nathana@fsr.com>
To: nanog@merit.edu
In-Reply-To: <DACACFED-C734-43B5-AFBD-3AB064BA218A@muada.com>
Errors-To: nanog-bounces@nanog.org
Iljitsch van Beijnum wrote:
> The problem is in the direction from M$ to you, so you can't fix that
> from your end. I wonder if they've installed SP3 on their servers...
Ah, you are right. I re-read the section on black-hole detection in
http://technet.microsoft.com/en-us/library/bb878081.aspx
more closely this time, and found that, yes, it only helps if the host
trying to send the large packets has the feature enabled:
"When PMTU black hole router detection is enabled, TCP tries to send
segments with the DF flag set to 0 after several retransmissions of a
segment are not acknowledged. If a segment with the DF flag set to 0 is
acknowledged, the MSS is decreased and the DF flag is set to 1 in
subsequent segments on the connection. Enabling PMTU black hole
detection increases the maximum number of retransmissions that are
performed for a given segment, and therefore has an effect on overall
performance."
I for some reason interpreted the advertisement of the black hole
detection feature as being a help to clients impacted by the inability
of the server to perform PMTUD.
--
Nathan Anderson
First Step Internet, LLC
nathana@fsr.com
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