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Does a router slow down transmission when buffers are full?

Recently had an issue where a routers buffers became full and only a reload fixed the issue. What was strange is that the there was a 100mb circuit between the 2 routers yet only 10meg was being used (CPU was at 100%). Soon as the reload was done it went back to normal, low CPU and average 40mb BW utilization. What i'm wordering or wanting to know is that when a routers buffers are full or CPU is at 100% is there any mechanism or protocol that gets sent to the data source to say hey, slow down with your tranmission and if so what is it? If not why didnt the source just send at the normal 40mb rate and let the destination struggle even more.


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Does a router slow down transmission when buffers are full?


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Not 100% clear what router buffers you referring to that became full.

About the closest feature that a router might use to notify the source to slow its transmission rate is ICMP source quench, but that a) not tied to router performance, as far as I know (although it could be tied to output queue drops) and b) generally not used anymore for various reasons.

As to why the sender slowed, if the sender was using TCP, it would slow its rate if it also saw packet drops and/or had to wait on ACKs.