tcpreplay completely bypasses the kernel TCP/IP stack when sending packets. In effect it writes almost directly to the network card itself. I'm not familiar with OpenOnload or ef_vi kernel bypass, but if I had to guess, the packets you are replaying are being dropped because the kernel thinks they are bogons. -- Aaron Turner https://synfin.net/ Twitter: @synfinatic Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. -- Benjamin Franklin
On Fri, Jul 8, 2016 at 11:22 PM, James deCocq <dotmar...@hotmail.com> wrote: > Ah, I should have mentioned that this is not a new application, it has and > does run regularly and successfully taking live multicast data via either > kernel sockets, or OpenOnload or ef_vi kernel bypass. The packet replay is a > new feature however, and works fine unless the application is configured to > use kernel sockets, in which case the kernel currently drops all the replayed > packets. Of course I confirm that the associated multicast group membership > is as expected prior to launching the replay. > > To confirm then, are you saying that tcpreplay should not interfere with the > IP stack in the scenario described; that being tcpreplay and application > running concurrently on the same box, tcpreplay out eth1 to switch, back to > eth2, kernel, and (hopefully) application? > > Thanks! > > ________________________________________ > From: Aaron Turner <synfina...@gmail.com> > Sent: Saturday, July 9, 2016 12:30:07 AM > To: Main forum for tcpreplay > Subject: Re: [Tcpreplay-users] replayed multicast packets dropped by ip stack > > The linux kernel IP stack won't deliver multicast packets unless you > open the appropriate listener socket. Obviously, without looking at > your application code I have no idea if that's your problem, but from > the sounds of it that is the most likely issue. Nothing you've said > sounds like a tcpreplay bug to me. > -- > Aaron Turner > https://synfin.net/ Twitter: @synfinatic > Those who would give up essential Liberty, to purchase a little temporary > Safety, deserve neither Liberty nor Safety. > -- Benjamin Franklin > > > On Fri, Jul 8, 2016 at 1:53 PM, James deCocq <dotmar...@hotmail.com> wrote: >> Hi all, >> >> NICETIES >> tcpreplay version: 4.1.0; CentOS 6.7; x86_64 >> Multiple Solarflare SFC9120 >> >> BACKGROUND: >> Our application can be built to use one of: >> * kernel sockets >> * OpenOnload (bespoke network stack, kernel bypass) >> * ef_vi (direct to/from VNICs, no stack) >> >> PROBLEM: >> * We test using tcpreplay of captured live multicast packets. >> * Replayed packets go out eth1 to the switch and back to eth2. >> * When application is built to use onload or ef_vi, it works as expected. >> * However when built for kernel stack, replayed packets arrive at eth2 >> as expected, but are subsequently dropped by kernel. >> >> DETAIL: >> * Multicast drops appear to originate from 2 spots in the linux stack: >> most from ip_rcv(), and some in tpacket_rcv() (the AF_PACKET stuff) >> * Captured live data is massaged for playback thusly, addresses redacted: >> tcprewrite -C --srcipmap=nnn.nnn.nnn.nnn/26:nnn.nnn.nnn.nnn >> --dstipmap=nnn.nnn.nnn.nnn/24:nnn.nnn.nnn.nnn/24 >> --enet-smac=00:0F:53:xx:yy:zz --enet-vlan=del -i in.pcap -o out.pcap >> * All mods and IP checksums look good in Wireshark, and again, >> the application receives expected flow if the kernel stack is not involved. >> >> QUESTION: >> * Of course I noted the caveat about replay on the same box; however >> I was not certain that the caveat applied to our use case, >> tcpreplay -> eth1 -> switch -> eth2 ->kernel; >> however drops from kernel's tpacket_rcv() would seem to suggest yes? >> * So is tcpreplay running concurrently with our application likely to be >> the cause of the kernel dropping multicast packets in this situation? >> >> Thanks very much for any assistance you can provide. >> >> james >> >> ------------------------------------------------------------------------------ >> Attend Shape: An AT&T Tech Expo July 15-16. Meet us at AT&T Park in San >> Francisco, CA to explore cutting-edge tech and listen to tech luminaries >> present their vision of the future. This family event has something for >> everyone, including kids. Get more information and register today. >> http://sdm.link/attshape >> _______________________________________________ >> Tcpreplay-users mailing list >> Tcpreplay-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/tcpreplay-users >> Support Information: http://tcpreplay.synfin.net/trac/wiki/Support > > ------------------------------------------------------------------------------ > Attend Shape: An AT&T Tech Expo July 15-16. Meet us at AT&T Park in San > Francisco, CA to explore cutting-edge tech and listen to tech luminaries > present their vision of the future. This family event has something for > everyone, including kids. Get more information and register today. > http://sdm.link/attshape > _______________________________________________ > Tcpreplay-users mailing list > Tcpreplay-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/tcpreplay-users > Support Information: http://tcpreplay.synfin.net/trac/wiki/Support > > ------------------------------------------------------------------------------ > Attend Shape: An AT&T Tech Expo July 15-16. Meet us at AT&T Park in San > Francisco, CA to explore cutting-edge tech and listen to tech luminaries > present their vision of the future. This family event has something for > everyone, including kids. Get more information and register today. > http://sdm.link/attshape > _______________________________________________ > Tcpreplay-users mailing list > Tcpreplay-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/tcpreplay-users > Support Information: http://tcpreplay.synfin.net/trac/wiki/Support ------------------------------------------------------------------------------ Attend Shape: An AT&T Tech Expo July 15-16. Meet us at AT&T Park in San Francisco, CA to explore cutting-edge tech and listen to tech luminaries present their vision of the future. This family event has something for everyone, including kids. Get more information and register today. http://sdm.link/attshape _______________________________________________ Tcpreplay-users mailing list Tcpreplay-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/tcpreplay-users Support Information: http://tcpreplay.synfin.net/trac/wiki/Support
