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Isn't it a sign of either a DOS attack or a network problem? I would guess that a restart of the service helps because, by closing the listening socket, you close the corresponding kernel SYN queue. Lukasz On Wed, Mar 16, 2016, at 00:39, Marian Zvada wrote: > Hi Folks, > > we're seeing these two types of kernel messages which are obviously > connected to xrootd process on US regional redirectors running on the > port 1094: > > --- > kernel: TCPv6: Possible SYN flooding on port 1094. Sending cookies. > kernel: possible SYN flooding on port 1094. Sending cookies. > --- > > This is happening intermittently on both US regional redirectors > cmsxrootd1.fnal.gov and xrootd.unl.edu. Both are behind DNS aliased host > cmsxrootd.fnal.gov. We're pretty confident that this typically occurs in > syslog when redirector is giving very long waits for access to files > through xrootd. > > Simple restart of service bring response time back to normal. We also > didn't notice any significant increase in use of memory nor cpu on the > machines itself so we're wondering if anyone from the list or developers > may explain if this is something to worry about. It is also hard to > catch so maybe if you have any idea what to watch next time and record > (besides core file) that'll help. Luckily, we at least know when we're > getting warning state of the xrootd-fallback SAM test this 'flooding' is > likely happening again... > > FNAL and UNL regional redirectors run xrootd-4.3.0-0.rc3.el6.x86_64 and > along slowness seen and odd kernel records in system logs there is > nothing obvious in the xrootd and cmsd logs to report. Maybe do you know > which specific xrootd process chain might trigger this kernel errors? > > Any feedback is very welcome! > > Thanks, > Marian > > ######################################################################## > Use REPLY-ALL to reply to list > > To unsubscribe from the XROOTD-L list, click the following link: > https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=XROOTD-L&A=1 ######################################################################## Use REPLY-ALL to reply to list To unsubscribe from the XROOTD-L list, click the following link: https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=XROOTD-L&A=1