Stephen.Clark at seclark.us
Mon Dec 10 13:22:16 PST 2007
Luigi Rizzo wrote:
>On Mon, Dec 10, 2007 at 11:22:33AM -0800, Chuck Swiger wrote:
>>On Dec 10, 2007, at 8:56 AM, rihad wrote:
>>>I'm having a hard time to understand what pipe queues are with
>>>respect to bandwidth limitation. ipfw(8) and dummynet(4) manuals
>>>didn't help me much.
>>Pipes and queues are two different things; a pipe simulates a network
>>link, and a queue is used to hold packets which are backlogged because
>>they are arriving faster than the outbound link (ie, a pipe) can
>>>How does dummynet's traffic shaping function?
>>It uses a variant of weighted fair queuing.
>actually the shaping uses a leaky bucket algorithm.
>The weighted fair queuing is the queue management scheme used
>when you have multiple queues attached to the same pipe
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Pipes are used to limit bandwidth. Queues are used to assign priority to
different classes of traffic. As an example
suppose you wanted to limit bandwidth for a specific ip to 2mbs. You set
up a pipe to do this and use ipfw to put traffic
from this ip into the 2 mbs pipe. If you then wanted to prioritize ftp
traffic at higher than priority than all other traffic for
this same user you would create 2 queues to feed the 2mbs pipe. You
would send the ftp traffic into the higher priority queue
and all other traffic for this user into the other queue.
"They that give up essential liberty to obtain temporary safety,
deserve neither liberty nor safety." (Ben Franklin)
"The course of history shows that as a government grows, liberty
decreases." (Thomas Jefferson)
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