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Date:	Thu, 22 Mar 2007 14:09:06 +0100
From:	Patrick McHardy <>
To:	Denys <>
	Stephen Hemminger <>
Subject: Re: iproute2-2.6.20-070313 bug ?

Denys wrote:
> /sbin/tc2 qdisc del dev ppp0 root 
> /sbin/tc2 qdisc add dev ppp0 root handle 1: prio 
> /sbin/tc2 qdisc add dev ppp0 parent 1:1 handle 2: tbf buffer 1024kb latency 
> 500ms rate 128kbit peakrate 256kbit minburst 16384 
> /sbin/tc2 filter add dev ppp0 parent 1:0 protocol ip prio 10 u32 match ip dst 
> flowid 2:1 

That is an incredible huge buffer value.

> qdisc tbf 2: parent 1:1 rate 128000bit burst 4294932937b peakrate
256000bit minburst 16Kb lat 4.2s

And it causes an overflow.

The limit for the TBF burst value with nanosecond resolution is
~ 4 * rate (10^9 * burst / rate < 2^32 needs to hold), resoluting
in a worst-case latency of 4 seconds. I think this limit is in the
reasonable range. Your configuration results in a worst-case
queuing delay of 64s, and I doubt that you really want that.

Obviously its not good to break existing configurations, but I
would argue that this configuration is broken.

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