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Date:	Wed, 03 Oct 2012 23:12:46 +0200
From:	Eric Dumazet <>
To:	Ken Savage <>
Subject: Re: RED tc qdisc not dropping?

On Wed, 2012-10-03 at 14:14 -0600, Ken Savage wrote:
> Hi there,
> I'm running openSUSE 12.2, using the machine as a router/WANsim device.
> Previously, I was running an older CentOS installation with a 2.6 kernel,
> and my tc-red commands ran just fine, and imposed some bandwidth constraint
> to the packets upon egress.  In 3.4.6, this doesn't seem to be the case
> any longer.
> Without any restrictions, there would be 25-30Mbps of traffic flowing out
> the interface -- this is to give you a sense of the data rate.
> Now, this said, I did notice that the latest RED code has the 'harddrop'
> option that I didn't have under CentOS with kernel 2.6.  So in my attempt
> to see ANYTHING happening with 3.4.6, I entered:
> tc qdisc add dev eth0 root red limit 40000 min 3000 max 9000 avpkt 1000 burst 5 harddrop probability 1
> Issuing 'tc -s -d qdisc show dev eth0', I obtain:
> qdisc red 8006: root refcnt 2 limit 40000b min 3000b max 9000b harddrop ewma 2 probability 0.73242 Scell_log 12
>  Sent 254028472 bytes 207494 pkt (dropped 0, overlimits 0 requeues 0)
>  backlog 0b 0p requeues 0
>   marked 0 early 0 pdrop 0 other 0
> All those zeroes seem a little amiss to me  ;)

Not sure I understand...

Why RED should drop a packet if there is no backlog ?

if you NIC has Gigabit speed, RED will allow Gigabit speed as well.

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