Cisco IOS IP SLA Traffic Generator

This topic is to discuss the following lesson:

Great post(s)! Thank you!

great work, Really useful info there,

Good post. Keep up the good work. Thanks.

Hi Rene
The image file named as “ethernet-ip-udp-payload-sizes.png” in this post is broken. It can not be displayed properly. If it is not my broadband problem, then your image file gets something wrong. Please check it.

Hi Hongfei,

Thanks for letting me know, I just re-uploaded this image.


Thanks a lot Renne you doing the things very easy. I have see that you don´t mention this on R2 activated “ip sla responder”.

In my case I can´t see traffic on the R2 if I haven´t this comand.


Hi Ruben,

If you want to see statistics with “show ip sla” then you’ll need to add the responder on the receiver. In this example, all I needed was to generate some traffic.


Hi Rene,

I was wondering, can a test like this be used to lets say sweep a range from lets say 16k to 1M on TCP or UDP and then check up until which load it was successful?
A test like that would be useful to have to measure the actual speed of a link like for DSL over ATM or metro ethernet.
I have always been looking for something like that.

Hi Edwin,

Hmm not really, to test something like this I would try iperf:


hi Rene,

yes iperf is great and probably one of the best tools out there for that purpose but i am looking for a way to test throughput from cisco to cisco without the use of external tool like iperf

i have been looking at ttcp but i cannot find enough doc to be able to pull off a simple throughput test brtween lets say 2 100mb links

i know it should be possible with ttcp but i just dont know how, this tool could be what i am looking for but i cannot find usefull info on the net on how to perform tests with it…

Hi Edwin,

I think I can create an example for TTCP but i’m not sure how useful it will be. From what I’ve read, it doesn’t use CEF but everything is process switched so it will be difficult to saturate a > 100 Mbps link with traffic.

If you are interested then I’ll create a writeup though.


Hi Rene,

You use ethernet frame header for calculations. Why you not take care of FCS(4 bytes) and EtherType (2 bytes)?. Total ethernet length shoud be :

8 bytes of preamble + 12 bytes MAC + 2 bytes ethertype/lengt + payload + 4 bytes FCS = 26 bytes + 20 bytes IP + 8 bytes udp = 54 bytes. So you shoud use a payload of 46 bytes for a total frame size of 100 bytes. Is not that right?

Thanks to you



Hi Diego,

There’s a difference between the L2 header and the “physically” transmitted frame. Here’s what belongs to the header:

Destination MAC: 6 bytes
Source MAC: 6 bytes
Ethertype: 2 bytes
FCS: 4 bytes

That’s 18 bytes in total.

The preamble (7 bytes) and start of frame delimited (1 byte) are not included with the L2 header.

Hope this helps.


Hi Rene,

What about MTU size ?


What about it? :slight_smile:

I had the same experience as Ruben above. I only saw traffic register on R2 in the policy map statistics when I added ip sla responder to R2’s config. I tested a couple of times (Cisco VIRL iosv version 15.6(2)T). Great tool though! I’ll definitely find this useful in my QoS studies.

HI Rene,

Thank you for your article. I was looking for something to generate traffic like 200Mbps or more. I’ve tried iperf seems is not good. Do you have anything else to suggest or any approach to configure inside the routers?

Hi Daniel,

Generating ~200 Mbps of traffic from the router will be difficult. I usually use Iperf for this, what went wrong with Iperf for you?

Rene, when you say 200 mbps is difficult, is it still possible? Or depends upon platform? Generating traffic from cisco end to end itself comes really handy when you have other Linux devices in between. I see the IP SLA options too for TCP too? Any idea will this work, whatever lower.