[c-nsp] difference between OutDiscards and Overruns

[Peter Rathlev]

On Wed, 2011-07-20 at 18:33 +0300, Martin T wrote:
> I see. So most likely Outdiscards happen in case of backplane puts
> frames to bus, but interface outbound buffers are not able to accept
> new frames because they are full?

Yes. Exactly where the drop occurs depends very much on the specific
hardware platform. On what device (and software) are you seeing this?

Outdiscards, often called "buffer drops", are simply a result of the
device trying to send more traffic out an interface than it can handle.
For example trying to send 120 Mbps out a 100 Mbps interface. The
interface buffers can store the excess traffic for some time, but when
they run out the interface starts to drop.

Keep in mind that these buffer drops are exactly what QoS is about:
dropping certain packets so there's room for others. (Simplified
version, since LLQ and EF is also about rearranging packets.)

-- 
Peter