netdev - Re: Proper value for bandwidth parameters

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Date:	Wed, 08 Feb 2012 10:10:36 -0600
From:	"Gregory G. Carter" <gcarter@...gi.com>
To:	"John A. Sullivan III" <jsullivan@...nsourcedevel.com>,
	netdev@...r.kernel.org
Subject: Re: Proper value for bandwidth parameters

Set nagios up and do a transfer over the line without TC controls.  Then use the figures from the line as a base for setting policy using TC.

This stuff is an art, not an idealized set of edges in a textbook on network theory.  So always see what your real capacity is before you set policy.

Gc

"John A. Sullivan III" <jsullivan@...nsourcedevel.com> wrote:

>Hello, all.  From a system administrator's perspective, do I need to
>reduce the values I feed to bandwidth defining parameters in tc such as
>the ul m2 values in HFSC?
>
>For example, if I have a 1.544 mbits circuit and I set HFSC ul m2 to
>1544kbits (or any other bandwidth parameter in different algorithms),
>when it calculates its timer for dequeuing the packet (let's assume a
>full sized 1500 byte packet) is it performing the calculation on 1500
>bytes or 1500 bytes plus overhead such as the Ethernet header, CRC,
>preamble, and IFG?
>
>I am assuming it is based upon the 1500 byte packet in the above
>example.  In which case, I think I need to reduce my bandwidth value fed
>to tc to account for the overhead lest I exceed the real bandwidth.  For
>example, the full sized Ethernet packet will be somewhere around 1538
>bytes so 1500/1538 * 1.544 = 1505kbits.  Is that correct? Is there a
>guideline for a multiplier to use? I suppose if we are flooding a link,
>it is most likely with full sized packets.  Thanks - John
>
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