Date: Thu, 22 Nov 2012 16:42:12 +0100 From: Marc Peters <marc@mpeters.org> To: freebsd-net@freebsd.org Subject: Re: Low Bandwidth on intercontinental connections Message-ID: <50AE47D4.7080608@mpeters.org> In-Reply-To: <50AE2686.8070007@xip.at> References: <50ACF62C.8000408@mpeters.org> <CAOgwaMuUuJ2%2BmKqsFVp=DyVFkfm8Et%2Brnt2iEGDO8i1Kt_kDVA@mail.gmail.com> <50ad087d.1892cc0a.2cce.3bf2@mx.google.com> <50AD1012.7020209@mpeters.org> <50AD14F8.8050001@xip.at> <50ADE5E4.9090708@mpeters.org> <50AE0B12.8000309@xip.at> <50AE1CCC.7080706@mpeters.org> <50AE2686.8070007@xip.at>
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On 11/22/2012 02:20 PM, Ingo Flaschberger wrote: > Am 22.11.2012 13:38, schrieb Marc Peters: >> interesting, the MTU is way lower, than i expected. Through the VPN >> tunnel, only 1322 bytes are possible without fragmentation. ScreenOS >> adds 42 additional bytes per paket and the FreeBSD box is receiving >> 1364 bytes, according to tcpdump. From the outside (only one Netscreen >> on the way), 1472 is the maximum possible size to send pakets without >> fragmentation (-D). Which MTU would you suggest to use? Shouldn't the >> MTU discovery of FreeBSD handle this correct? > > do you see fragmented tcp packets on the receiving site in tcpdump? nearly every packet is fragmented, if i read th [TCP segment of a reassembled PDU] correct. Those have a length of 1364. Thera are also lots of [TCP Window Update] (every two to three acks from the receiving host, where the tcpdump took place). After some time, there were lots of [TCP Dup ACK] from the receiving host and the throughput went to a crawl and had lots of retransmissions. After 30 sec. everything went back to "normal" as of transmitting pakets without dubs and retransmissions. The same tcpdump collect on the Linux hosts, the packets had a length of 1514 and no dubs or retransmissions. I didn't get the option JUMBO_MTU removed, but removing TSO4 didn't changed anything. Adding packetfiltering and the pipe didn't change anything, too. > > When you load the tcpdump data (tcpdump -s 1500 -w filename ...) into > wireshark, you can graph the speed (bit/sec, packets/sec) and do some > more tcp analysis. > > Kind regards, > Ingo Flaschberger > _______________________________________________ > freebsd-net@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org"
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