cvs commit: src/sys/netinet tcp_syncache.c

Andre Oppermann andre at
Thu May 24 19:49:53 UTC 2007

Gleb Smirnoff wrote:
> On Thu, May 24, 2007 at 01:36:49AM +0200, Andre Oppermann wrote:
> A>  Yes, these logs can be triggered remotely.  Broken packets and spoofed
> A>  packets may cause them.  We're interested in the former.
> A> 
> A>  I'll do some benchmarks on the impact of the logging and then decide
> A>  whether to put it under a sysctl.
> A> 
> A>  The reason it is unconditionally enabled is to see if non-compliant
> A>  TCP stacks are out there that fail the very strong (but fully RFC and
> A>  TCP-secure conform) checks.
> A> 
> A>  W/o logging we have no way of really knowing.  Before we were possibly
> A>  accepting stuff we shouldn't have (spoofing and attacks).  Now we may
> A>  drop stuff we perhaps should accept anyway.  W/o logging diagnosing a
> A>  TCP problem was very difficult and would need a lot cooperation with
> A>  the PR submitter, if it was submitted at all.  We normally only got a
> A>  report of TCP 'not working'.  Figuring out what went wrong was pretty
> A>  much doing iterative shots into the dark and see if something squeaks.
> A> 
> A>  With logging I want to make things much more obvious and simpler to
> A>  diagnose.  Plus we get information in cases (from admins reading the
> A>  logs) that were totally lost in the noise or not even attempted to
> A>  be debugged.
> A> 
> A>  For our TCP maintainers (mostly I at the moment) and also 3rd parties
> A>  this makes TCP trouble diagnosis much more accessible.  Based on a
> A>  log report and the OS name/version of the remote end we can pretty
> A>  much tell right away what went wrong.  This saves an order of a
> A>  magnitude in debugging and fault analysis time.  From many hours and
> A>  email round trips to mere minutes and one or two information requests.
> I completely understand that this logging is very important in the
> process of refactoring the TCP code. I just think that the performance
> impact should be measured before merging this logging to RELENG_6.

Currently I don't have any plans to MFC the TCP changes.


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