Common operational misconceptions

Steven Bellovin smb at
Tue Feb 21 01:40:33 UTC 2012

>> The timer for Linux is 5 minute by default but you can change it.
> Timer timeouts do not affect TCP MSS.

RFC 2923:
      TCP should notice that the connection is timing out.  After
      several timeouts, TCP should attempt to send smaller packets,
      perhaps turning off the DF flag for each packet.  If this
      succeeds, it should continue to turn off PMTUD for the connection
      for some reasonable period of time, after which it should probe
      again to try to determine if the path has changed.

It's Informational, not standards track, but the problem -- and the fix
-- have been known for a very long time.

		--Steve Bellovin,

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