QoS - exceed-action transmit

[amp512_nyph]

Hi Folks,

Cisco 4500-X do not support egress queing on VLAN interfaces (SVI) which means cannot do a traffic-shapping, is there a work around via policing? I can police the traffic and then on the trunk interfaces do "per-port-per-VLAN" QoS but again only the policing not shapping so I was wondering what is the effect of "exceed-action transmit" command

policy-map SHAPE

class class-default

  shape-average 8000000

Versus...

policy-map POLICE

class class-default

  police 8000000 4000 conform-action transmit exceed-action transmit

Thanks.

[Bilal Nawaz]

Hello, exceed-action is the action to take on packets when exceeded the rate limit. You have the transmit key word so it will transmit anything exceeding your police statement. (i.e. pass traffic as normal)

Normally you use exceed-action drop or violate-action drop, where anything to the limit permitted, but anything past the limit will be dropped.

Hope this helps.

http://www.cisco.com/en/US/docs/ios/12_2/qos/command/reference/qrfcmd8.html

Please rate useful posts and remember to mark any solved questions as answered. Thank you.

[Joseph W. Doherty · Accepted solution]

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Posting

If you need to shape, you really don't want to police.  Both regulate transmission rate, but shaping buffers excess while policing just drops excess.

It's not surprising a SVI doesn't support egress queuing as SVI often have multiple ports.  Assuming a 4500-X is somewhat similar to other 4500s, ports should support some kind of port egress QoS, but they may not support shaping.  Many switches don't.

The common purpose of the exceed-action-transmit, it's often used to mark over rate packets.  It can also be used to accumulate stats on over rate packets.

[amp512_nyph]

Thanks guys, is there a way to achieve results (if not same close enough) of shaping but via policing and by manipulating Bc and Be plus the "exceed-action"? My fear is if the packet is dropped the congestion avoidance and slow-start would kick in and then the transmit rate would slow down significantly, so I was wondering if "exceed-action" is set to "transmit" that way there are no drops but of course carrier would police and drop anything over our CIR. This is for L2 service from a telco for 40-50 remote locations and 4500-X is at the head-end.

[acampbell]

Atrey,

Have a look at this link re Shaping V Policing.

http://www.cisco.com/en/US/tech/tk543/tk545/technologies_tech_note09186a00800a3a25.shtml

They are different

Regards,
Alex.
Please rate useful posts.

[Joseph W. Doherty]

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

Thanks guys, is there a way to achieve results (if not same close enough) of shaping but via policing and by manipulating Bc and Be plus the "exceed-action"? My fear is if the packet is dropped the congestion avoidance and slow-start would kick in and then the transmit rate would slow down significantly, so I was wondering if "exceed-action" is set to "transmit" that way there are no drops but of course carrier would police and drop anything over our CIR. This is for L2 service from a telco for 40-50 remote locations and 4500-X is at the head-end.

No, you're not going to be able to emulate shaping with a policer.

What you can do is set you policer to match whatever values your service provider provides.  Then at least, you'll have stats for drops that tend to be hidden by the provider.

Or, place another device, in-line, that supports shaping.

[amp512_nyph]

Thanks Joseph If a typical spoke is 10Mbps CIR, we shaped them at like 8Mbps on the hub but now I can police exactly at CIR-10Mbps? Do policing create bandwidth inefficiencies?

[Joseph W. Doherty]

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

You should be able to police at the 10 Mbps CIR assuming you know the providers Tc.  (Often difficult to find out.)

No, policing isn't inefficient, but often default configurations don't emulate a like interface with sufficient buffers.  I.e. policing often drop packets out of bursts that a like speed interface would have queued.

[amp512_nyph]

Joseph,

Back to what you just mentioned "I.e. policing often drop packets out of bursts that a like speed interface would have queued." even if I exceed the conformed CIR, Bc however if the action is set to "transmit" my port should not drop packets?? I know my carrier would This was my original question but learned a lot, thanks again.

To your other point about "default config don't emulate a like interface with sufficient buffers" I figured since I am dealing with data trafffic (no voice at least for now), I would settle on a Tc say 125ms to get my Bc. So from above example if CIR is 10Mbps Bc = 10000000*.125 = 1250000 or if I don't know carrier's Tc I should not police at full CIR?

[Joseph W. Doherty]

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

Back to what you just mentioned "I.e. policing often drop packets out of bursts that a like speed interface would have queued." even if I exceed the conformed CIR, Bc however if the action is set to "transmit" my port should not drop packets?? I know my carrier would  This was my original question but learned a lot, thanks again.

Yes, you're correct, if you explicitly transmit the over rate packets, they're not dropped.

To your other point about "default config don't emulate a like interface with sufficient buffers" I figured since I am dealing with data trafffic (no voice at least for now), I would settle on a Tc say 125ms to get my Bc. So from above example if CIR is 10Mbps Bc = 10000000*.125 = 1250000 or if I don't know carrier's Tc I should not police at full CIR? 

A Tc of 125ms should behave better than the default Tcs (older IOS used 25ms newer use 4ms[?]).  As to what the carrier will do, you would have to ask them.  Likely they will police at the CIR unless they allow you to burst over.  If they do, important question is what Tc do they use.

[amp512_nyph]

Joseph,

You are right I shouldn't say "no egress queuing" I should have said "no egress queueing on anything other than physical interfaces". So it can definitely do Shaping but on physical interfaces. I can do "per port per VLAN" policing, which is basically 8021q trunk port  but not sure about shapping on that.

Thanks.