Hardware Queues

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Apr 2nd, 2010
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Hey Guys,

Can anyone tell me if there is a way to check how many hardware queues a particular interface has?  I'm just trying to dive into deeper understanding of the architecture and have not found much documentation from cisco on it.  I've got a 3745 with an NM-4T card and when doing 'show controllers' I only see one entry for tx_ring yet I've heard that these cards use two hardware queues.  One for broadcasts and the other for unicast traffic.

Does anyone have an idea that could help me?

Thanks in advance for your assistance!!!


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Federico Coto F... Fri, 04/02/2010 - 15:40
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Someone please correct me if I'm wrong, but as far as I know the router has only a single hardware queue (which is always FIFO unless using a Serial interface which is WFQ).

If using QoS, then you can have several software queues to treat traffic in a different way. But HW is only one.


Lei Tian Fri, 04/02/2010 - 19:07
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Hi Dave,

As Federico said, for software based router, there is only one hardware queue, the tx-ring for each physical interface. The tx-ring is a pointer, which points to the memory where packet actually store at.

For hardware based switches, the queueing structure is different per platform or linecard. The number of queues can be vary from 3 to 8.


Lei Tian

d.serra Sun, 04/04/2010 - 08:37
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Yeah...it looks exaclty as you said with Serial interfaces having only one hardware queue.  I was watching a Class on Demand video from IPExpert on QoS and he said serial interfaces have 2 hardware queues, one for broadcast and one for unicast.  The only thing I found on the internet referencing this was a post where someone also mentioned the two queues and they two found no documentation on it.  I'm wondering if only certain Serial hardware has this unique architecture and Cisco just hasn't documented it well.

Here is the link I mentioned:



paolo bevilacqua Sun, 04/04/2010 - 11:44
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There is only one hardware queue for serial interfaces. All the other are software constructs, and different people may refer to them with different names.


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