Rare project developers

[Alexander Gall <>]

Hi Carmen

The -n and -k options don't do what you think they do when you use
TCP. Iperf uses a buffer of a certain size when reading and writing
data. By default it uses 128KiB for TCP, see the description of the
--length option.

The -k parameter is in units of that buffer size and you can see that
with -V:

: gall@lepton[gall]; iperf3 -c bsmp1 -k 1 -V | grep Starting
Starting Test: protocol: TCP, 1 streams, 131072 byte blocks, omitting 0 
seconds, 1 blocks to send, tos 0
: gall@lepton[gall]; iperf3 -c bsmp1 -k 2 -V | grep Starting
Starting Test: protocol: TCP, 1 streams, 131072 byte blocks, omitting 0 
seconds, 2 blocks to send, tos 0

So with -k 1000 you actually send 1000*128KiB of payload data (the
total amount includes all TCP overhead). The number of packets depends
on the MSS and the number of retransmits.

I'm not sure what exactly -n does with TCP.

--
Alex

On Tue, 28 Jun 2022 11:55:46 +0200, Carmen Misa Moreira 
<> said:

> Hi,
> I'm using iperf3 with the -k flag to send 1000 packets:

>     root@itcs-p4srv-02:/home/mmisamor# iperf3 -c 2001:1458:301:cd::100:3d8 
> -L 32772 -p 5204 -i 10 -k 1000 &
>     [1] 74718
>     root@itcs-p4srv-02:/home/mmisamor# Connecting to host 
> 2001:1458:301:cd::100:3d8, port 5204
>     [  5] local 2001:67c:2c4:1::2 port 45904 connected to 
> 2001:1458:301:cd::100:3d8 port 5204
>     [ ID] Interval           Transfer     Bitrate         Retr  Cwnd
>     [  5]   0.00-0.11   sec   124 MBytes  9.09 Gbits/sec  202    683 KBytes
>     - - - - - - - - - - - - - - - - - - - - - - - - -
>     [ ID] Interval           Transfer     Bitrate         Retr
>     [  5]   0.00-0.11   sec   124 MBytes  9.09 Gbits/sec  202             
> sender
>     [  5]   0.00-0.12   sec   121 MBytes  8.81 Gbits/sec                  
> receiver
   
>     iperf Done.
   
> But on the switch I received more than 1k packets -> 1713 packets:

>     E513-E-YECWH-1#show access-list acl_all_ipv6_flowlabels
>          tx          rx                  timers
>     seq  byte  pack  byte        pack    last      timout    cfg
>     10   0+0   0+0   0+0         0+0     never     00:00:00  all any all 
> any all flow 131076&261884
>     11   0+0   0+0   0+0         0+0     never     00:00:00  all any all 
> any all flow 65540&261884
>     12   0+0   0+0   0+0         0+0     never     00:00:00  all any all 
> any all flow 196612&261884
>     13   0+0   0+0   0+165006    0+1713  00:00:01  00:00:00  all any all 
> any all flow 32772&261884
>     20   0+0   0+0   0+0         0+0     never     00:00:00  all any all 
> any all flow 131072&261632
>     21   0+0   0+0   0+0         0+0     never     00:00:00  all any all 
> any all flow 65536&261632
>     22   0+0   0+0   0+0         0+0     never     00:00:00  all any all 
> any all flow 196608&261632
>     23   0+0   0+0   0+0         0+0     never     00:00:00  all any all 
> any all flow 32768&261632
>     29   0+0   0+0   0+0         0+0     never     00:00:00  all any all 
> any all flow 5201
>     30   0+0   0+0   360+256420  5+2268  00:00:01  00:00:00  all any all 
> any all
   
> So I was wondering if there is something regarding fragmentation or 
> something that causes this mismatching in the values, I would expect to
> have 1k packets on the P4 switch in this case. I saw the same behaviour if 
> I use the flag -n to send 1000 bytes:

>     root@itcs-p4srv-02:/home/mmisamor# iperf3 -c 2001:1458:301:cd::100:3d8 
> -L 32772 -p 5204 -i 10 -n 1000 &
>     [1] 74722
   
>     root@itcs-p4srv-02:/home/mmisamor# Connecting to host 
> 2001:1458:301:cd::100:3d8, port 5204
>     [  5] local 2001:67c:2c4:1::2 port 45908 connected to 
> 2001:1458:301:cd::100:3d8 port 5204
>     [ ID] Interval           Transfer     Bitrate         Retr  Cwnd
>     [  5]   0.00-0.00   sec   106 KBytes  7.06 Gbits/sec    0   13.9 KBytes
>     - - - - - - - - - - - - - - - - - - - - - - - - -
>     [ ID] Interval           Transfer     Bitrate         Retr
>     [  5]   0.00-0.00   sec   106 KBytes  7.06 Gbits/sec    0             
> sender
>     [  5]   0.00-0.00   sec  13.9 KBytes   105 Mbits/sec                  
> receiver
   
>     iperf Done.
   
> I received 900 bytes:

>     E513-E-YECWH-1#show access-list acl_all_ipv6_flowlabels
>          tx          rx            timers
>     seq  byte  pack  byte    pack  last      timout    cfg
>     10   0+0   0+0   0+0     0+0   never     00:00:00  all any all any all 
> flow 131076&261884
>     11   0+0   0+0   0+0     0+0   never     00:00:00  all any all any all 
> flow 65540&261884
>     12   0+0   0+0   0+0     0+0   never     00:00:00  all any all any all 
> flow 196612&261884
>     13   0+0   0+0   0+900   0+10  00:00:12  00:00:00  all any all any all 
> flow 32772&261884
>     20   0+0   0+0   0+0     0+0   never     00:00:00  all any all any all 
> flow 131072&261632
>     21   0+0   0+0   0+0     0+0   never     00:00:00  all any all any all 
> flow 65536&261632
>     22   0+0   0+0   0+0     0+0   never     00:00:00  all any all any all 
> flow 196608&261632
>     23   0+0   0+0   0+0     0+0   never     00:00:00  all any all any all 
> flow 32768&261632
>     29   0+0   0+0   0+0     0+0   never     00:00:00  all any all any all 
> flow 5201
>     30   0+0   0+0   0+4037  0+38  00:00:12  00:00:00  all any all any all
   
> Best regards,

> Carmen Misa

-- 
Alexander Gall, Network

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