Metod, but shouldn't the Iperf client send out traffic at 500Mbps as I had "-b 500m" specified? In my example is prints unrealistic bandwidth(~60Gbps) results.
regards, Martin On 8/21/14, Metod Kozelj <[email protected]> wrote: > Hi, > > Martin T je dne 21/08/14 15:12 napisal-a: >> if I execute "iperf -c 10.10.10.1 -fm -t 600 -i 60 -u -b 500m" and >> 10.10.10.1 is behind the firewall so that Iperf client is not able to >> reach it, then I will see following results printed by Iperf client: >> >> [ ID] Interval Transfer Bandwidth >> [ 3] 0.0 - 60.0 sec 422744 MBytes 59104 Mbits/sec >> [ 3] 60.0 - 120.0 sec 435030 MBytes 60822 Mbits/sec >> etc >> >> >> Why does Iperf client behave like that? Is this a know bug? > > That's not a bug in iperf, it's how UDP is working. The main difference > between TCP and UDP is that with TCP, IP stack itself takes care of all the > > details (such as in-order delivery, retransmissions, rate adaption, ...), > while with UDP stack that's responsibility of application. The only > functionality that iperf application does when using UDP is to fetch the > server (receiving side) report at the end of transmission. Even this > function > is not performed in perfect way ... sending side only waits for server > report > for short time and if it filled network buffers, this waiting time can be > too > short. > > The same phenomenon can be seen if there's a bottleneck somewhere between > the > nodes and you try to push datarate too high ... routers at either side of > the > bottle will discard packets when their TX buffers get filled up. If TCP was > > used, this would trigger retransmission in IP stack and all of > TCP-slow-start > would kick in and sending application would notice drop in throughput. If > UDP > was used, IP stack would not react in any way and application would dump > data > at top speed. > -- > > Peace! > Mkx > > -- perl -e 'print > $i=pack(c5,(41*2),sqrt(7056),(unpack(c,H)-2),oct(115),10);' > -- echo 16i[q]sa[ln0=aln100%Pln100/snlbx]sbA0D4D465452snlb xq | dc > > ------------------------------------------------------------------------------ > > BOFH excuse #252: > > Our ISP is having {switching,routing,SMDS,frame relay} problems > > ------------------------------------------------------------------------------ Slashdot TV. Video for Nerds. Stuff that matters. http://tv.slashdot.org/ _______________________________________________ Iperf-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/iperf-users
