Hi.

how many shaping queues exist on a router? in the book, the author mentioned that there must be 2 shaping queues; i know the first might be WFQ queue. but what is another one? and if we can use LLQ in shaping scenario, does LLQ replaces with original WFQ? ... I'm a bit confused about shaping!!

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ciscoworlds.com
timaz mohsenzadeh

I thought the most common queuing was FIFO.

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- Pete

I read about shaping queue. but for clarity, i need more obvious answer. maybe one of the queues is FIFO and another is WFQ. am I right?

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ciscoworlds.com
timaz mohsenzadeh

Well... FIFO isn't a shaping queue it's just how packets are handling normally but it's still a queue.

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- Pete

For serials the default is WFQ. Ethernet defaults to FIFO.

I've got no correct and obvious answer yet!

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timaz mohsenzadeh

Shaping is one thing and queueing is another thing, so shaping queues make no sense. WFQ is a type of queueing, and LLQ is anothe type of queueing.

If you configure traffic shape the traffic can be delayed in a buffer, may be you are refererring to this buffer?

Most routers have a single hardware queue (aka a ring buffer) that holds the next packet to be sent. I'm not certain if there are routers that have two hardware queues, but it seems possible.

If you configure any sort of queuing and/or shaping, you'll have multiple software queues that will be used to buffer the packets so that the software can use a QoS policy to decide from which queue to draw from to refill the ring buffer. The number '2' doesn't play a role here.

On a switch, the queues aren't as flexible. You're generally limited to 4 queues (such as 1p3q == 1 priority queue and 3 general purpose queues).

don't think so, at least not that i've read about.

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"If you're good at anticipating the human mind. It leaves nothing to chance."
-Jigsaw

finally, I found the answer from "QoS cert guide, by Cisco press"; that's the answer if you are interested in:

you know that there are 2 kind of queses : software queses (like LLQ, CBWFQ) and hardware (tx) queue. first point is that there is always 1 hardware queue (which is called TX queue too). when shaping is enabled, "a single special kind of queue, named Shaping Queue, is created between software queues and TX queue. this Shaping queue is using FIFO.
just another situation exists that will make router to create another kind of Shaping Queue, called "Dual FIFO" queue and that occurs when we use FRF.12 (which makes fragmentation possible) on the interface. in this situation, instead of "Single FIFO software Shaping Queue", we will have "Dual FIFO" queue. first queue inside this "Dual FIFO" queue, will accept packets sent by LLQ and the second one inside this "Dual FIFO" queue will accept fragments of other packets sent by non-LLQ queues. I hope this help you all

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ciscoworlds.com
timaz mohsenzadeh