Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I test bandwith with iperf. I set up UDP protocol.

I'm trying to setup limit from 10 to 100 megabit/s. Until 90 megabit max speed is correct.

When I write -b 100m or don't write this speed become only 50 megabit/s. Why?

share|improve this question

UDP doesn't have transmit pacing, congestion backoff, and the other features TCP has. If you don't implement them, throughput will suffer terribly -- that's why TCP implements them.

Iperf doesn't have the necessary logic to find the maximum UDP transfer rate. You would need to increase the rate so long as all packets were getting through and back off when packets started dropping to find the maximum rate. Iperf doesn't do this, but you can configure a rate and see how well it works.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.