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I have created a UDP file using Scapy and I'm using tcpreplay to send the packet. I've faced two weird issues:

  1. The number of packets sent is not identical to the (--pps) parameter. Not sure if the answer is (http://tcpreplay.appneta.com/wiki/faq.html#why-doesnt-tcpreplay-send-traffic-as-fast-as-i-told-it-to)
  2. When I send less packets, i.e --pps=10, the CPU load is higher when I send more packets, i.e. --pps=200. I was expecting the other way around.

BTW, I'm using tcpreplay version 3.4.4

Frak
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Tom
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1 Answers1

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Issue 1. many --pps issues fixed in latest Tcpreplay version

Issue 2. CPU utilization is improved with latest version, but you can still expect to see 100% CPU being reported. In reality CPU utilization is over reported when using -t or --mbps=0 options. In these cases Tcpreplay will yield the sending thread whenever the TX buffers are full. This causes Tcpreplay to become the scheduler for the CPU. The result is a reported 100% CPU, however other processes on the CPU remain responsive.

fredk
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  • Hi @fredk I have updated Tcpreplay to the latest and got better result. However, after 70000 p/s, the rate is not accurate anymore. Do you know why ? The CPU of the sender is not reaching the limit nor it's close. – Tom Jul 11 '17 at 02:54
  • Multiply the average size of your packets by 8, then by 70000 packets/sec. Does it exceed the line-rate of your card? In my lab, I can get full 10GigE rates at expected rates by adjusting --pps. But once the link is saturated, increasing --pps will make it go faster. – fredk Jul 11 '17 at 20:52
  • @fredk I am using the latest version `4.3.2 (build git:v4.3.2)` but when I use even pps=10 or less, I get packet loss when pinging through the same interface. It doesn't look like it is handling it well. I've even lowered its `nice` value in htop but still getting ping packet loss. – Frak Jul 02 '19 at 20:13
  • I suggest that you fill out a [bug report](https://github.com/appneta/tcpreplay/issues) so you can document OS, exact parameters used and screen scrapes. – fredk Jul 03 '19 at 23:46