Date: Mon, 26 Jun 2017 15:13:43 -0700 From: Matt Joras <matt.joras@gmail.com> To: Navdeep Parhar <nparhar@gmail.com> Cc: Youssef GHORBAL <youssef.ghorbal@pasteur.fr>, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: Re: Sporadic TCP/RST sent to client Message-ID: <CADdTf%2BgeCy4naC5jJ6UhTm7-n9c6XKpgRs96EsXGq-UVjSn8MQ@mail.gmail.com> In-Reply-To: <CAPFoGT8sthFOm=vOiFb9%2B2BM=%2BBqtREz1SrOm_UiVge81CrYrw@mail.gmail.com> References: <84CB0795-B28E-46DF-9593-4C1BAAB7DDF5@pasteur.fr> <CAPFoGT8sthFOm=vOiFb9%2B2BM=%2BBqtREz1SrOm_UiVge81CrYrw@mail.gmail.com>
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Out of curiosity, what sort of lagg setup are you using that's causing the TCP packets to be split across the two lagg interfaces? Matt On Mon, Jun 26, 2017 at 1:35 PM, Navdeep Parhar <nparhar@gmail.com> wrote: > On Thu, Jun 22, 2017 at 3:57 PM, Youssef GHORBAL > <youssef.ghorbal@pasteur.fr> wrote: >> Hello, >> >> I'm having an issue with a FreeBSD 11 based system, sending sporadically TCP/RST to clients after initial TCP session correctly initiated. >> The sequence goes this way : >> >> 1 Client -> Server : SYN >> 2 Server -> Client : SYN/ACK >> 3 Client -> Server : ACK >> 4 Client -> Server : PSH/ACK (upper protocol data sending starts here) >> 5 Server -> Client : RST >> >> - The problem happens sporadically, same client and same server can communicate smoothely on the same service port. But from time to time (hours, sometime days) the previous sequence happens. >> - The service running on server is not responsible for the RST sent. The service was deeply profiled and nothing happens to justify the RST. >> - tcpdump on the server side assures that packet arrives timely ordered. >> - the traffic is very light. Some TCP sessions per day. >> - the server is connected using a lagg enslaving two cxgb interfaces. >> >> In my effort to diagnose the problem (try to have a reproductible test case) I noticed that the issue is triggered most likely when those two conditions are met : >> - the ACK (in step 3) and the PSH/ACK (in step 4) arrive on different lagg NICs. >> - the timing between those two packets is sub 10 microseconds. >> >> When searching the interwebs I came across a strangely similar issue reported here 7 years ago : >> https://lists.freebsd.org/pipermail/freebsd-net/2010-August/026029.html >> >> (The OP seemed to have resolved his issue changing the netisr policy from direct to hybrid. but no reference of laggs being used) >> >> I'm pretty sure that I'm hitting some race condition, a scenario where due to multithreading the PSH/ACK is somehow handled before the ACK making the kernel rising TCP/RST since the initial TCP handshake did'nt finish yet. >> >> I've read about netisr work and I was under the impression that even if it's SMP enabled it was made to keep prorocol ordering. >> >> What's the expected behaviour in this scenario on the netisr side ? >> How can I push the investigation further ? > > I think you've already figured out the situation here -- the PSH/ACK is likely > being handled before the ACK for the SYN because they arrived on different > interfaces. There is nothing in netisr dispatch that will maintain protocol > ordering in this case. > > Regards, > Navdeep > _______________________________________________ > freebsd-net@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org"
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