Wiliam: Please read the section on unidirectional transfers. Your udp capacity might be constrained by the nic - then again, maybe you need to change your operands... https://users.soe.ucsc.edu/~kent/test/udpcast.html ________________________________ From: William Oquendo &lt;woquendo(a)gmail.com&gt; Sent: Tuesday, July 6, 2021, 11:34 p.m. To: Brent Kimberley Cc: udpcast(a)udpcast.linux.lu Subject: Re: Two or more clients drops bandwith by 2 orders of magnitude Hi, thanks for your answer. Do you mean making sure of that when doing the test by using udpcast? in that case how? I cannot find explicitly how to do that in the manual. In any case I re run the test (after a power failure) and things are scaling better now, as expected. I do not know why ... Thanks for udpcast On Sat, Jul 3, 2021 at 5:17 AM Brent Kimberley <Brent.Kimberley@durham.ca<mailto:Brent.Kimberley@durham.ca>> wrote: William Please ensure you are using UDP/IGMP. Brent Hi, (I hope this list is still active) I am a newbie. I am testing multicast support on three computers connected through a gigabit switch. When only the server, ran as (rand.bin is a 1Gb file) udp-sender --interface eth1 --file rand.bin and ONE client udp-receiver --file rand.bin are connected, the bandwidth is around 937.32 Mbps, which is very good. But with two or more clients if consistently drops to 11 Mbps I would expect to bandwidth to decrease as 1/N, where N is the number of clients. What am I missing? I am using a dumb switch. Thanks -- Best regards / Cordialmente, William-Fernando Oquendo -------------------------- Este correo puede carecer de tildes o e?es debido al teclado. THIS MESSAGE IS FOR THE USE OF THE INTENDED RECIPIENT(S) ONLY AND MAY CONTAIN INFORMATION THAT IS PRIVILEGED, PROPRIETARY, CONFIDENTIAL, AND/OR EXEMPT FROM DISCLOSURE UNDER ANY RELEVANT PRIVACY LEGISLATION. No rights to any privilege have been waived. If you are not the intended recipient, you are hereby notified that any review, re-transmission, dissemination, distribution, copying, conversion to hard copy, taking of action in reliance on or other use of this communication is strictly prohibited. If you are not the intended recipient and have received this message in error, please notify me by return e-mail and delete or destroy all copies of this message. -- Best regards / Cordialmente, William-Fernando Oquendo -------------------------- Este correo puede carecer de tildes o eñes debido al teclado. THIS MESSAGE IS FOR THE USE OF THE INTENDED RECIPIENT(S) ONLY AND MAY CONTAIN INFORMATION THAT IS PRIVILEGED, PROPRIETARY, CONFIDENTIAL, AND/OR EXEMPT FROM DISCLOSURE UNDER ANY RELEVANT PRIVACY LEGISLATION. No rights to any privilege have been waived. If you are not the intended recipient, you are hereby notified that any review, re-transmission, dissemination, distribution, copying, conversion to hard copy, taking of action in reliance on or other use of this communication is strictly prohibited. If you are not the intended recipient and have received this message in error, please notify me by return e-mail and delete or destroy all copies of this message.