TCP MSS configuration and throughput question

[Vidhya Raman]

I am trying to verify single elephant flow throughput on my Device under test by running a TCP proxy on DUT and setting up TCP connections using ASTF mode and the script http_eflow2.py

I am running Trex v2.82 on a 18 core Intel Xeon server "Intel(R) Xeon(R) Gold 6240 CPU @ 2.60GHz" and I have two XL710 ports between x86 server and DUT.

I setup MSS of 8948 and I start the tests and I captured pcap file and I see that the TCP packet sizes are 2242Bytes.  It looks like Trex buffers are limited to 2242bytes. Is there anyway to configure larger buffers on Trex.

Also for a single elephant flow, I see a maximum throughput of 2.4Gbps. when I start traffic using the command

/t-rex-64 --astf -f astf/http_eflow2.py -m 10 -d 1000 -c 1 -l 1000 -t size=800,loop=100000,win=512,pipe=1,mss=8948

Changing the multiplier does not result in higher throughput. Is there any limitation in Trex ?

Thanks

Vidhya

[hanoh haim]

Hi Vidhya, 

Did you try the same in loopback (without your DUT)?

There should *not* be a limit for MSS. I will look into it. 

Try to have a bigger window and bigger chunk ( size should be bigger than win)

size = 2048,win=1024 maybe there  is a RTT that requires a higher window size. 

multiplier will not help as this is one flow. 

Another thing, have a look into the TCP counters to see if there is an issue there

Thanks

Hanoh