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Silver

QoS Performance Hit on Fixed-Chassis L3 Switches

I'm not sure how to spec an appropriate switch based on it's CPU performance when performing QoS duties.

The switch must police ingress traffic on a single interface, based upon the destination IP subnet. Normally, I'd spec a router and that would be straight forward enough. But, in this instance, it would instead be useful to use a fixed chassis switch.

Both the 3850 and 4500-X series use MQC, which is a good start. But, how can I work out if they can cope with 100Mbps of ingress traffic when it's all being punted up to the processor?

I'd like to assume the worst in terms of packet sizing, and be sure I'm covered.

Any help appreciated...

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Super Bronze

Re: QoS Performance Hit on Fixed-Chassis L3 Switches

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

Normally on a small L3 switches, QoS features are supported by the hardware.  When they are, figure capacity as you might if QoS wasn't being used on the L3 switch.

In cases where traffic on the L3 switch is punted to the main processor, you have a problem.  Often the main processor on a L3 switch has less, perhaps much less, raw CPU performance vs. a software based router.  (This because, also normally, the main CPU only needs to perform control plane functions, not data plane functions.)  Generally, vendors don't even provide performance specs for a L3 switch's CPU performance.

2 REPLIES
Super Bronze

Re: QoS Performance Hit on Fixed-Chassis L3 Switches

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

Normally on a small L3 switches, QoS features are supported by the hardware.  When they are, figure capacity as you might if QoS wasn't being used on the L3 switch.

In cases where traffic on the L3 switch is punted to the main processor, you have a problem.  Often the main processor on a L3 switch has less, perhaps much less, raw CPU performance vs. a software based router.  (This because, also normally, the main CPU only needs to perform control plane functions, not data plane functions.)  Generally, vendors don't even provide performance specs for a L3 switch's CPU performance.

Silver

Re: QoS Performance Hit on Fixed-Chassis L3 Switches

Thanks Joseph. Too many late nights this week I think. I should have remembered this, but thanks again anyway.

It would be hard to work out if a small L3 switch will handle any given IGP network then. Fortunately, not something I need to worry about this time.

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